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Urban settlements delimitation in low-density areas—An application to the municipality of Tomar (Portugal)
Landscape and Urban Planning 97 (2010) 156–167
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Urban settlements delimitation in low-density areas—An application to the municipality of Tomar (Portugal) José Antunes Ferreira ∗ , Beatriz Condessa, Joana Castro e Almeida, Pedro Pinto Centre for Urban and Regional Systems (CESUR), Instituto Superior Técnico (IST), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 2 November 2009 Received in revised form 10 May 2010 Accepted 25 May 2010 Available online 6 July 2010 Keywords: Urban sprawl Land-use planning Buffer method Consolidated urban areas
a b s t r a c t One of the major issues in land-use planning is how to contain urban sprawl. To this effect, plans integrate new regulations and mechanisms that severely limit construction outside urban perimeters and restrict the areas available for expansion within the settlements. Before enforcing these restrictions, a review and correction of existing delimitation of settlements was necessary. The new limits were established through the identification of effectively consolidated urban areas. In the absence of official criteria defining them, this paper presents a methodology establishing the limits of these consolidated areas. Based on the identification, in a Geographical Information System (GIS) of existing buildings, and incorporating the analysis of road network, social facilities, and physiographic constraints (such as floodplains or steep slopes), several criteria were defined so as to delimit the urban settlements. A review of other methodologies is presented as a contextualization of the proposed one, but it is not the focus of the paper to specifically contrast or appreciate them. The study area is the municipality of Tomar, in Central Portugal, a territory with very disperse human occupation. Having achieved an accurate delimitation of the settlements’ current extent that reflects the purposes of rational land-use, the settlement delimitation was successfully revised so as to mirror the current occupation. Also, the objectivity and clarity of the adopted criteria, and its applicability to the whole municipality, allowed the methodology to be unanimously well received by the Municipal Government and Parish Councils, even if it deals with a somewhat politically delicate subject. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The publication, in 1998, of the Law for the Policy on Territorial Management and Urbanism (LBPOTU—Lei n◦ 48/98, de 11 de Agosto) established, for the first time in Portuguese Law, the general principles and goals that should steer this policy. Arising from a context of growing degradation of landscapes and natural resources, due to the scattered and unplanned occupation of vast areas, in the periphery of the main urban centres or in rural areas, the delimiting of urban perimeters rapidly became one of the main concerns for the first generation of Municipal Land-use Plans (PDM). Some of the principles stated in the LBPOTU directly address this issue, by recommending a sustainable use of the land and the weighed and sparing use of natural resources, according to the principle of economy. One of the expressed objectives of the LBPOTU is “The rational use of natural resources, the preservation of the environmental
∗ Corresponding author. Tel.: +351 218 418 305; fax: +351 218 409 884. E-mail addresses: [email protected] (J.A. Ferreira), [email protected] (B. Condessa), [email protected] (J. Castro e Almeida), [email protected] (P. Pinto). 0169-2046/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2010.05.007
balance, the humanization of the cities and the improved functionality of built-up areas”. Therefore, the human occupation of the territory should be restricted to the areas deemed as necessary for the satisfaction of housing shortages and those spaces necessary for economic activities and urban functions. Also, there should be an adequate provision of infrastructures and facilities, the main purpose being the increased equality in the access to the said infrastructures and facilities, while guarantying a minimal increase in the environmental impact. Among the objectives listed in the LBPOTU, it is stated that there should be a quest for: • “the economic sustainability of the infrastructures, avoiding unnecessary extension of both the networks and urban perimeters and promoting rational urban infill”; • “the preservation and protection of soils best suitable for agriculture or forestry, restricting the shift to other uses only when markedly necessary”. In a situation of economic and spatial restrictions, this will be reflected in the need to ensure slower expansion of urban areas, instead promoting their densification and consolidation, and limiting or prohibiting construction outside urban areas (that is, in ‘rural
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Fig. 1. The Médio Tejo Region and the municipality of Tomar.
land’). Beforehand, however, it is essential that a clear and objective identification of the continuous built-up areas, or ‘urban continua’, be made. This way, all the constructions therein will subsequently be included in revised urban perimeters, determined by the new PDM. Whenever the continua fulfil criteria related to dimension or compactness they will be recognized as consolidated urban settlements. The PDM is the instrument through which the development strategies and options stated on national and regional level plans and programmes are transferred to locally applicable regulations and land-use plans and policies, according to the Portuguese urban
law. Several PDM are currently under revision and, as with the first generation of PDM, the land-use regulations (and, specially, their consequences over building permits) on which the spatial organization of the territory is based is again assuming a front-role, attracting the highest scrutiny from both elected representatives and local population. In the revision of the PDM for the municipality of Tomar (Central Portugal, located in the Oeste and Vale do Tejo Region) it has been clearly stated that the priority should be given to the consolidation of existing settlements and the focus on housing rehabilitation instead of new construction and urban sprawl.
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Fig. 2. Current delimitation of urban perimetersand scattered construction.
It is therefore the main objective of this paper to present a methodology to delimit consolidated areas. This methodology will be applied to the municipality of Tomar within the context of the PDM revision. After the application of the present methodology, delimiting the consolidated areas, the identification of the final urban perimeters, including urban expansion areas, may be completed.
2. Study area: Tomar municipality
The municipality has a population of around 43K inhabitants. With a area of about 350 km2 , it is both one of the biggest and among the most populous municipalities in the region. The city of Tomar has a population of about 16K inhabitants. Together with its suburbs the city accounts for little less than half the total population of the municipality, whereas the second biggest settlement has just above 1K. Of the municipality’s 208 settlements, only 9 have over 500 inhabitants and 180 have less than 250 inhabitants, which gives a good measure of how scattered the population is (CESUR, 2008).
2.1. Location 2.2. The Municipal Land-Use Plan (PDM) of Tomar The objective of the current methodology is the delimitation of urban settlements in the municipality of Tomar. This municipality is located in central Portugal, in the transition between the central south-western lowlands and Tagus valley and the more mountainous central Portugal. The municipality is therefore very diverse, in terms of the relief, landscapes, and patterns of land-use. It is part of the Médio Tejo NUTS III, within the Centro NUTS II region. Set slightly to the interior of the main axis of north–south connection (the main corridor between the metropolitan areas of Lisbon and Porto), it is nevertheless located at the intersection of two important major roads (IC3 and IC9) and is served both by the main railway line and a branch line (Fig. 1).
The current PDM of Tomar, approved in 1994 (Câmara Municipal de Tomar, 1994), was produced among the first generation of Portuguese Municipal Land-Use Plans. At the time, and right after new legislation was approved, the PDM were not yet mandatory, but there was a generalized move towards their creation, on the behalf of the municipalities. This was encouraged both by special incentives being awarded to those municipalities that already had PDM (financing for infrastructures and facilities) and restrictions to the municipalities’ powers in, for instance, declaring public interest for expropriation purposes, that were thenceforth subject to the existence of a valid PDM.
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Fig. 4. Urban perimeters with unbalanced expansion areas.
Fig. 3. Examples of problems arising from the use of outdated base maps (a considerable number of dwellings already existent were not considered for the 1994s delimitation).
It is now clear that the PDM gave a major contribution towards the formation of a new cultural mind-set regarding planning issues. This process opened a window for the debate of urban planning and land-use management issues and concepts, finally creating space for consultation and negotiation in the planning process. Simultaneously, though, insufficiencies were revealed, both in the level of formation of the technicians involved and the lack of the technical data necessary for better validating the plans. Tomar was no exception and, while the first PDM was being produced, the delimiting of the urban perimeters was done resorting to very outdated geographic information and without the assurance of an adequate incorporation of suggestions made by the Juntas de Freguesia (Parishes) and private owners. As a result, several inconsistencies were identified in the present urban perimeters (Fig. 2). The municipality of Tomar presents a very scattered human occupation of the territory. The permissive development laws for ‘rural’ land, as stated by the Municipal Land-use Plan (PDM) of 1994, have in fact contributed to aggravate this form of occupation (Fig. 2). The urban perimeters delimited by the current PDM (1994) generate four complex and evidently unfair situations (Figs. 3 and 4), both towards the rights of private owners and in conflicting with the objectives stated in the LBPOTU. These factors were by no means exclusive to Tomar; much to the contrary. For one, the difficulty in coping with new legal demands was felt by most municipalities, unprepared to deal with such issues, and many Portuguese municipalities face similar problems with unsuitable urban delimitations. Also, the surge of new construction in formerly remote rural areas is an almost universal phenomenon in those areas located near the edge of large urban areas’ influence, as described in several works dealing with patterns of land-use in these rural areas under influence of urban areas—the “urban fringe” described by Bryant et al. (1982). Lewis and Maund (1976) already stated in the mid-70s that “the increasing urbanization of the countryside is a process which all advanced societies are experiencing at the present time. As a consequence the once simple and distinct division between rural and urban no longer applies”.
In the case of Tomar, the “fringe” effect is of a double nature, as the municipality itself is located at the edge of Lisbon Metropolitan Area’s influence. This contributes to a very strong push towards construction in former rural areas, as studied by Stern and Marsh (1997), Goffette-Nagot and Schmitt (1999) and Goffette-Nagot, 2000), Garreau (1991), Antrop (2000, 2004) and Lucy and Philips (1997). Even if the want of an individual landowner to build on his property is understandable, permitting it would generate both the degradation of the landscape, as is already the case with some areas of Tomar, and even issues of equal-opportunities and rights in the face of the law. Antrop (1998) reflects upon these issues, having in mind Western European examples: “Here, land is regarded as property over which the owner possesses a free right of use. The impact of individual landowners depends upon their status, reflected by the size of their property and the means to maintain or transform it. The impact of small landowners will be restricted to small areas, such as their garden or places they use for recreation. Although the effect upon the change of the global landscape might seem minimal, these small impacts must be multiplied by the large number of individual landowners. The result of this can be seen in the new landscapes”. The main consequences to Tomar’s settlement patterns were, on one hand, the heavy dispersal of construction and, on the other, the Table 1 Some rules for construction in rural classes: ‘forestry’, ‘forestry and agriculture’ and ‘agriculture’, as defined by the PDM of Tomar. Rural classes
Some construction rules
‘Forestry and Agriculture’ or ‘Forestry’
• “Construction of house for the farmer, as long as the agricultural or agro-forestal unit has an area over 2 ha and there is a contribution to the better working conditions”: minimum area for the unit – 1500 m2 ; maximum floor-area, including annexes – 300 m2 , etc. • Construction of isolated buildings for housing: minimum plot area – 3000 m2 ; maximum gross floor-area ratio – 0.05, etc. • When there are constructions within 30 m of the projected location of the new building and the plot is served by a paved road or street and basic infrastructure, the municipality may allow the building on plots smaller than 3000 m2 . • Building for housing by plot: minimum plot area – 5000 m2 ; maximum gross floor-area ratio – 0.04; maximum floor-area – 250 m2 , etc. • When there are constructions within 30 m of the projected location of the new building and the plot is served by a paved road or street and basic infrastructure, the municipality may allow the building on plots smaller than 5000 m2 .
‘Agriculture’
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Table 2 Synthesis of urban agglomerations delimitation methodologies. Methodology
Criteria and limitations
Morphological delimitation
Defined by N.U.R.E.C. 1994 (Network on Urban Research in the European Community), it takes into consideration the United Nations’ concept for contiguous built-up area, where the distance between buildings must be less than 200 m. That is, by generating a buffer of 100 m around buildings it is possible to delimit built-up continua. This sort of criteria, well suited to cities with very uniform expansion, is insufficient when these processes are a complex blend of suburbanization, sprawl and the incorporation of existing settlements. Strictly morphological criteria for the definition of a city proved insufficient in an age of stark suburbanization. Methods based on population density were then developed for the purpose of defining urban agglomerations. The delimitation methodology developed by GEMACA (Group for European Metropolitan Area Comparative Analysis) in 1996 consists in the application of 3 criteria: the economic core is the set of contiguous units with more than 7 jobs per ha and more than 20,000 jobs; the morphologic agglomeration is the set of contiguous units with more than 7 inhabitants per ha and more than 60,000 inhabitants, and the functional urban region (hinterland) is the set of units with over 10% commuting to the economic core. Cladera (2003) presents a number of applications that resort to this methodology. One of the first was that of the Census Bureau of the United States of America, from 1950, and is still the basis for the definition of Metropolitan Areas in that country. Then, the criterion used was that of aggregating all counties with at least 2/3 of the active population working in non-agrarian functions. In 1959 the Institute of International Research defined a metropolitan area as containing both a central city, or nucleus, with over 50K inhabitants and the contiguous administrative units that had a fraction of non-agrarian jobs above 2/3. The total population should be above 100K. In 1970, Cafiero et al. defined the metropolitan area as having more than 100K inhabitants, 35K or more non-agrarian workers and a job density for non-agrarian functions of 100 jobs/km2 . McDonald (1987) presents another methodology of this type, focusing on the identification of urban employment subcentres. Involves the analysis of commuter flows (home/work place) and economic and social criteria. The COMET internet site presents the criteria developed by the IinterregIIC-project ‘Group for European Metropolitan Areas Comparative Analysis’ (GEMACA II). In this project 14 Functional Urban Regions in North-Western Europe were analysed by using a delimitation according to economic core of metropolitan area (sets of contiguous units with more than 7 jobs per ha and more that 20,000 jobs), hinterland (set of units with 10% or more commuting to economic core), population (total population >1 million) and cores (monocentric and polycentric cores are possible).
Demographic delimitation
Delimitation based on the economic and social structure
Functional delimitation
deficient consolidation of the planned expansions, caused by the rapid and unplanned manner through which these were created (Fig. 2). The current regulation, contained in the PDM, may have worsened the scattered construction, by allowing construction in land classified as rural. (see, for example, the articles 28 and 29 of the PDM specified in Table 1). Thus, building is basically allowed in a plot located in spaces destined for agriculture or forestry agriculture whenever the area exceeds 3000 m2 . In this case (and most plots in Tomar will fulfil the criteria), the building of a house with a floor-area of 150 m2 is easy. The mentioned rules, coupled with the existence of a strong pressure for construction of some housing types, generated a strong
surge in the number of requests for building permits outside urban perimeters. The dominating typologies are the detached singlefamily housing, both in the close vicinity of urban settlements or on the outskirts of the city of Tomar, and the isolated singlefamily house, aimed for the weekend- or summer-house market. The parishes of Tomar in which this weekend- or summer-house typology assumes greater importance are precisely those that are farther from the city. In the meetings held with the parish councils, as part of the consultation procedures of the PDM’s revision, it was gathered that this second-house belonged mostly to individuals that had their roots in the area but lived and worked outside the municipality (that is, emigrants, but of local origin). On the other hand, those new houses located near the reservoir of the Castelo de Bode Dam were mostly destined for ‘outsiders’, not originally from the area. The lack of an adequate supply of building plots within urban perimeters or the difficulty in acquiring them from landowners unwilling to either build on them or sell them to those who will, may have contributed to the strong building pressure outside urban settlements. The slim supply of housing in the city of Tomar and the slow or stalled rate of conclusion of some large-scale urban plotting and urban plans situated inside the city’s boundaries were also indentified as probable causes for this sprawl. The need to update and extensively revise the urban perimeters, adjusting them to the present reality of the municipality became, as well as evident, essential to the subsequent stages of the PDM revision. 2.3. The Regional Plan for the Oeste e Vale do Tejo (PROT-OVT) During the current revision of Tomar’s PDM, the intention to strengthen and consolidate existing settlements has been repeatedly stated, instead of the definition of over-dimensioned expansion areas and construction in “rural” land, avoiding, whenever possible, the linear extension along the roads. This is, in fact, one of the main concerns of the Regional Plan for the Oeste e Vale do Tejo (PROT-OVT), a planning instrument of higher hierarchy, to which the PDM must conform. Two of the planning principles stated by the PROT-OVT (CCDRLVT, 2008) are: • Concentration of constructions: The PDM should establish models for land-use that promote the concentration of construction in urban settlements or rural clusters, adequately identified and delimited for this purpose. This should serve as to avoid all forms of scattered and linear expansion and excessive extension of the settlements, pursuing instead the reconversion, restructuring or rehabilitation of existing built-up areas, already served by infrastructures and facilities; • Contention, proportionality and programming of urban areas: The PDM should dimension and program the structuring and consolidation of urban land in accordance with the real needs, current and projected, taking into account different types of demand for housing, economic activities and other urban functions. The PROT-OVT also identifies a set of norms for the identification of new urban areas or the creation of expansion areas for existing settlements, along with criteria for classifying land as urban instead of rural. A ‘consolidated urban area’ is a cluster of at least 80 buildings for housing or other urban uses, in continua that have a building density of at least 7 buildings per hectare. As for the different classes of rural land, the PROT-OVT warns against the widespread permission of single-family houses’ construction in isolated plots. It recommends instead their concentration in low-density settlements and rural clusters that follow the dominant traditional patterns of rural communities, as well as
J.A. Ferreira et al. / Landscape and Urban Planning 97 (2010) 156–167 Table 3 Urban settlements delimitation. Country and references
Criteria
Netherlands (Statistics Netherlands) Leeuwen (2006, 2007)
Population cluster map: morphological delineated area; mainly groups of residential houses; recognizable street pattern (no ribbon development); form one cluster when: separated by less than 200 m (>200 m when connected by bridge); minimum number of dwellings.
Grid method: • total number of dwellings per grid (dwellings from housing register with addresses; addresses provided with coordinates); • proximity factor (each cell calculated a proximity factor).
Finland (Statistics Finland) Kanerva (2001)
Localities are clusters of buildings housing at least 200 residents, where the distance between buildings normally does not exceed 200 m. It takes into account buildings other than residential buildings, i.e. buildings used exclusively for work places. However, it does not include buildings used for agricultural production. Hospitals and other institutions situated outside localities are included only if the number of their resident staffs, including family members, is at least 200 (hospital patients are not taken into account). The method creates a grid where cells that hold residential buildings are selected. These are aggregated whenever contiguous and converted to polygons. A buffer is generated, with a distance based on the number of residential and non-residential buildings contained in the cluster of built-up cells to ensure all buildings are fully included. Buffering merges the adjacent polygons together if they are closer than two times the value of distance from one another.
Step 1: Buildings, grid and buffered grid polygons: “urban” cells within the grid are selected, based on them containing a given number of dwellings. Contiguous “urban” cells were merged together, forming clusters defined by polygons.
Step 2: Selecting building blocks inside the area of influence of a locality: areas with 200 people were picked out. To find building blocs in close contact with a locality, a buffer zone was formed and the polygons inside or touching the buffer line were picked out.
Step 3: Merging polygons together by buffering: The polygons were merged to the main area by buffering.
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Table 3 (Continued ) Country and references
Criteria
Step 4: Resizing buffer zone back to original: To obtain the final form of the locality, the buffer zone was resized back to its original dimension.
Norway (Statistics Norway) Dysterud (1999)
An urban settlement in Norway is defined as an agglomeration having at least 200 residents, and where the distance between the houses – as a rule – does not exceed 50 m.
promoting the reuse of derelict housing and rehabilitation of the existing housing. An exception is made to real working farms, but with a much narrower understanding of what the minimal area for the farm should be. The enforcement of the regulations stated by the PROT-OVT does therefore strengthen the need to better define the urban continua.
3. Methodology for the delimitation of urban settlements 3.1. Existing methodologies A set of methodologies is used by several authors (Ferrão et al., 2002; Cladera, 2003; Ramos and Silva, 2007) for the delimitation of urban agglomerations, as systematized in Table 2. These are organized into four main types of delimitation methodologies that address slightly different aspects or constraints in base-information by using very different criteria for segregating or merging areas so as to generate the urban agglomeration. It is not the purpose of the following to discuss the overall merits of each methodology, but simply to provide a brief overview. This aims at synthetically analysing what alternative methodologies are there, and whether they are appropriate to low-density urban settlement delimitation in Tomar’s context. By incorporating, among other criteria, concentrations of employment and economic influence defined by commuting, these methodologies are not adequate for small urban settlement delimitation. Most settlements under analysis have only about 80–250 inhabitants, with residual urban economic activity. Nevertheless, some of the concepts aforementioned can be, and were, explored in defining the methodology for small settlement delimitation—concepts such as the definition of population thresholds, or the identification of the average distance between buildings in urban context, by way of buffer generation, as used in morphological delimitation. Satellite images are fast becoming a good instrument for the delimitation of agglomeration areas but arguably not for the scale of analysis required for these very small settlements located in areas of scattered construction. The remote sensing or digital processing of satellite images is indeed used in defining metropolitan agglom-
erations in various works, such as Bosselmann (2008), Donnay et al. (2001) or Mesev (2003), but focusing on large metropolitan areas delimitation and comparison or segregation of urban land-use at a large scale. Until recently, the resolution was also insufficient for detailed urban delimitation, as noted by Pauleit and Duhme (2000). With the spectacular improvement in the spatial resolution of commercially available satellite imagery, it is perfectly conceivable the substitution of aerial photos in the very near future. There is, nevertheless, a traditional reliance on rectified aerial photography, that has led most municipalities to acquire and regularly renew this base-information at affordable costs. This was the case with Tomar, where this type of imagery had been acquired recently and therefore was made the obvious choice for settlement delimitation. Much in the same way, the methodology that combines Synthetic Aperture Radar (SAR) and optical data for urban mapping, developed by Corbane et al. (2008), proved inadequate to the scale and financial constraints of local planning. The more traditional digital processing over aerial photography, as referenced for instance in Webster and Beckett (1970) or Falkner and Morgan (2002), was therefore both the more economical and practical solution. Given the choice of orthorectified aerial photography as the source of imagery, the methodology would have to be adjusted to the available sources of digital data, and specifically to the analysis of the existing buildings and their clusters. Closer to the local scale that is required for Tomar, a few methodologies were analysed, developed by statistics agencies from Finland, the Netherlands and Norway (Table 3), that address comparable issues. These methodologies adopted by the statistics offices are very similar to the methodology presented in this paper, both in scope and in the steps taken to achieve the delimitation of settlements (define clusters of housing and then merge, through buffering, all clusters within a given distance of each other). Nevertheless, they fail to address (as it was not the purpose of the statistics offices’) issues strictly related to spatial planning, such as: the inclusion of the aforementioned morphologic constraints to building (e.g. slopes, floodplains); the protection of natural resources (e.g. riverbeds, protected land); whether or not the areas were served by the road network; or if social facilities were to be aggregated to the settlements.
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Table 4 Methodology steps.
1st Step
Previous condition: Generate a buffer of 25 m around each existing building and identify clusters of buildings (whenever the buffers meet) → only clusters with over 25 buildings in continuum are considered as ‘consolidated areas’. The 25 m used in generating the buffers were the result of an analysis done over digital maps and crossed with on-site observation of the building patterns in rural Tomar. Several other buffer distances were iterated but 25 m buffers (a distance below 50 m between two buildings) were those that more closely reflected the observed continua and breaks. The 25-building clusters correspond to an adaptation of the rules contained in the PROT-OVT.
2nd Step
Identify urban streets: All roads located within the cluster defined in the previous step.
3rd Step
Generate a buffer of 50 m around the urban streets. This will define the basic limit for the ‘consolidated area’. The following steps define exceptions that may alter this first limit.
4th Step
Whenever there is a gap of at least 70 m without any building on one of the sides of the street, the limit is pushed back to the street. These 70 m correspond to the sum of the 25 m buffers along the road, from each of the bordering buildings, and the 20 m gap that is considered to be the threshold for a continuum to exist.
5th Step
When there are non-built-up areas located within the limit that qualify as REN (floodplains or slopes with an incline of over 25%) or RAN, the limit will exclude any area located over 6 m away from existing buildings—just enough to guarantee some minor imprecision on the maps will not carry legal consequences over building rights for existing houses.
6th Step
Whenever two clusters are located no more than 20 m apart, they may be merged, whenever there is not the need to guarantee the safeguard of ecological corridors or the limiting of over-long linear development.
7th Step
Include within the limit buildings that were part of the original (1994) urban perimeter, maintaining their status as “urban” constructions. In these cases, the limit is drawn so as to include the building and a buffer of around 6 m, linking it to the limit defined by the previous steps.
8th Step
Whenever a public facility is located within a 50 m distance to the previous limit, the latter will be extended so as to include the facility within the ‘consolidated area’. The 50 m are the result of adding to the 25 m buffer to the last building in the settlement a 50 m walking distance to the facility.
Another methodology reviewed is that described by Valentim (2007), based on spatial statistics (grid method), for the identification of clusters with more than a certain threshold of discrete elements located in contiguous locations (e.g. houses), by identifying local densities for each cell with the grid.
This methodology was also used in the context of settlement identification in the municipality of Tomar, but analysed only the urban and suburban areas of the city, and not the smaller rural settlements, thus requiring adaptation. Even so, the methodology is very similar to the one hereby describe, except for the criteria
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adopted (such as buffer distances and the inclusion of new spatial planning criteria), and in that the present methodology waves a fully automated spatial statistics methodology. The adoption of this semi-automatic application of the chosen criteria became obvious due to the unavailability of sufficiently accurate digital information for some of the more relevant aspects of spatial planning. Among these, were such items as the geomorphologic constraints or the existence of social facilities near a settlement, which it would render a fully automated application exceedingly complex. 3.2. Proposed methodology for the identification of consolidated areas 3.2.1. Input data The methodology developed in part around the existing sources and current municipality’s databases, so as to minimize the costs involved and to allow for a quicker incorporation of updates. Upfront, the most detailed image of existing construction, and the one that is constantly being updated by the municipality’s urban planning services (Departamento de Planeamento Físico) is a digital database, based on the vectorization of rectified aerial photographs. This digitalization is done on ArcView GIS software (©ESRI) roughly every year, based on the availability of new aerial surveys. The latest version is based on aerial photos dating back to 2007, which provide the best information possible on the current situation. Most other relevant information used as a basis for the delimitation is also provided in ArcGIS formats (shape files and databases), and this was also the software used in implementing the methodology described hereafter. Some other relevant information provided both by the municipality’s services and by government institutions, was also provided mostly as shape files or other ArcGIS file formats. These include the Digital Terrain Model and relief map with contour lines at 5m intervals; base-information for the Ecological National Reserve (REN), including steep slopes and floodplains, and the Agricultural National Reserve (RAN); shape files with streams, reservoirs and social facilities; and the 1994 cartography from the original PDM. All digital data was projected on one of the official projection systems for Portugal, the Datum 73 IPCC Hayford-Gauss. The final output is expected to comply to only a 1:25,000-scale detail, but the present delimitation is obviously unmanageable at such a scale, given the minute size of most of the elements under analysis—a much more detailed analysis is therefore required. A precision of around 1.5–2 m is achievable using the software and base data available, even though the required accuracy for the final output maps will be of only 12.5 m. Nevertheless, this enhanced precision will be helpful for other applications of the obtained results, such as day-to-day land-use planning and analysis of requests for building permits by the municipal services. 3.2.2. Method steps To best characterize the current structure of settlement of the municipality of Tomar, a methodology was developed for delimiting precisely today’s extents of the consolidated areas of each urban area. This is paramount to the definition of the ‘rural’ or ‘urban’ classification of the land. The objectivity, universality and transparency of the methodology were deemed as crucial and the defined criteria led to following steps (Table 4): The first 3 steps define the polygon within which the urban continuum is enclosed. Steps 4-through-8 allow for the incorporation in the methodology of essential exceptions. The 5th step, for instance, concerns the protection of natural continua and corridors. The capability of identifying and removing the more environmentally sensitive areas from the urban perimeters will prove fundamental to the subsequent definition of the municipal eco-
logical network. This network’s definition is an integral part of the PDM’s revision, and the need to protect the corridors therein is sustained, among many others, by Fedorowick (1993) or Ahern (1991). 3.3. Results The results produced by applying the methodology, defining the consolidated urban areas and the comparison between these and the perimeters for the Urban Settlements as defined by the 1994 PDM are presented in Fig. 5, with the indication of areas that superimpose between both delimitations and those that differ: areas pertaining to the 1994 limits that were identified as not being part of a consolidated area and those that were not part of 1994 urban perimeters but are currently consolidated urban areas. It should be emphasized that the consolidated urban areas closely reflect the de facto settlement of the municipality, obtained through the analysis of existing buildings and settlements. In fact, even though the methodology was, at first, developed without having the criteria contained on the PROT-OVT, still unavailable at the time, the methodology proved to closely conform to them with resource to minimal adaptation, which seems to confirm its adequacy to the principles that guided the PROT-OVT and the criteria therein. Some key results of the methodology’s application to the municipality of Tomar are presented in Table 5. Although one of the main preoccupations during the inception stages of the methodology was that, by recognizing pre-existent settlements or houses just outside the 1994 perimeters a significant increase in the total urban area might occur, the results were, somewhat surprisingly, quite the opposite. Although the number of settlements increased from 197 to 208 – by rectifying situations where urban continua were beforehand ignored – the total urban area did not. In fact, it was significantly reduced, by almost one-quarter. Despite the reduction in total urban area, the number of buildings encompassed by the new limits increased from around 30,000 to almost 37,500. This means 77.4% of all the buildings fall within the consolidated urban settlements, as opposed to only around 62% with the previous delimitation. The proposed methodology and the results produced by its application to the municipality of Tomar were presented to the municipal council, the Regional Development Coordinating Commission (CCDR-LVT) and the 16 parish councils, in a series of meetings held between July and September 2008. The several representatives had a positive reaction both to the methodology and the results obtained. It was also stated the need for a second iteration of the methodology after the incorporation of updated geographical information, concerning buildings constructed after 2004, which may change a few details in the delimitation of some consolidated areas. These should produce but small alterations, according to a preliminary analysis done with the assistance of municipality’s services and Parish Councils. Nevertheless, by having resorted to GIS technology, the process of delimiting was both much more efficient and quick than traditional methods but will also allow for a simple updating of the results, when new information becomes available. The determination of some of the values, such as the distance between buildings or the averaged depth of the plots, was subject to an iterative process, taking into consideration the distinct characteristics of the different areas of the municipality of Tomar, and proved adequate for the delimitation of the consolidated areas, closely reflecting the concerns and complaints made by the parish councils in relation to the 1994 delimitation. The evident effort made to eliminate all subjective criteria and to closely fit the methodology to the reality verified in the munic-
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Fig. 5. Comparison between consolidated urban areas (2008) and urban perimeters as defined by the PDM (1994).
Table 5 Comparison between the delimitation of urban settlements by the 1994 PDM and the application of the present methodology.
Number Total area (ha) Buildings Number % of Total
Urban Settlements delimited in the 1994 PDM
Consolidated urban settlements
197 3.844
208 2.906
30.390 62.7
37.489 77.4
ipality ended up mostly coinciding with the confirmation and correction of several unjust situation or errors in the previous delimitation and already identified both by the parish and municipal councils. As such, and since the subjectivity of previous efforts was eliminated, the methodology was unanimously accept by these political bodies. 4. Discussion and conclusions The main driving force behind the proposed methodology was the need to correct the errors detected in the previous delimita-
tion done in the 1994 Municipal Land-Use Plan (PDM) of Tomar. The limits drawn by that PDM brought about evident injustice: the exclusion of houses located right next to urban settlements’ limits, and the virtual unavailability of plots for new construction within the boundaries of some historically important settlements, were readily identified as critical issues that needed to be addressed by the PDM’s revision. The proposed methodology intended to obtain maximum acceptance, both by the municipal council, municipal assembly and the parish councils, while simultaneously reflecting the Regional Plan guidelines that stress the need to contain scattered construction and urban sprawl and to consolidate the urban system. Having finally achieved an accurate delimitation of the urban settlements’ current extent, it will then be possible to establish expansion areas that directly reflect the purposes of rational land-use, in accordance with the LBPOTU. The priority will be given to the consolidation of the existing urban structure, namely through the identification of a clear urban system hierarchy. Therefore, it will be possible to enforce or reinforce clusters of public facilities and services that may, along-side an enhanced public transport system, allow for a better coverage of the demand in
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remote rural areas of the municipality. This will also permit a more rational use of limited public funding. The methodology had very precise targets and budgetary constraints in mind, but this was by no means a limitation to its overall coherence and pertinence to the land-use analysis that was its main objective. Reviewing other methodologies proved useful, but none fulfilled the necessary criteria. To give an example, the buffer method used by the Norwegian Statistics Office, presented earlier, is very similar to the present one, but does not, for instance, encompass situations where social facilities are in close proximity to a settlement. In all the methodologies analysed, some very relevant issues pertaining to the field of spatial planning, such as the incorporation of physiographic constraints (e.g. slopes, floodplains) were not considered—due to the mainly statistical nature of most methods. It was also evident, even beforehand, the inevitability of migrating the delimitation process from the traditional analogical methods, over printed maps, to a semi- or fully automated method. The advantages of GIS use in contexts of shifting land-uses, especially in urban areas or rural areas under urban influence is well documented, in such works as Holden and Turner (1997), Dai et al. (2001), Li (2004) or Lópeza et al. (2001). The need to include this level of analysis in the criteria for the settlements’ delimitation led to a semi-automatic approach, as some of the data was virtually impossible to analyse in a fully digital process. Some of the more significant limitations of the methodology are: • the need to constantly update the main GIS database with new information, such as new buildings or shifts in land-use; • the possibility that a given new building may generate new spatial relations between different clusters – suggesting the merging of two settlements – may be difficult to cope with bureaucratically and cause significant shifts in the total urban area of a given parish; • even though information on the specific function of each of the buildings’ polygons was available (e.g. housing, warehouses, industries, etc.), the reliability of the information was insufficient for this typological classification to be incorporated into the criteria. Nevertheless, in case there is a scrutiny of the data that will ensure its accuracy, new criteria may be added effortlessly into the methodology, such as the separate analysis of industrial and residential clusters, or the identification of commercial centres. The methodology includes some innovations and adaptations, in relation to the other reviewed methodologies: • the simple and straight-forward approach towards data analysis, tailor-made to suit the ready-available base-information, while maintaining the preciseness of the results and technical standards intact; • the objective being the determination of “net” urban areas, all major urban voids within the settlements are excluded, thus defining more accurately the effectively built-up areas, unlike the methodologies adopted by the statistical offices; • the methodology includes steps that analyse, and allow for the exclusion of, physiographic constraints, such as steep slopes, best agricultural soils or floodplains; • the base-information, being essentially all available from the municipality’s services and government institutions, is inexpensive; • it is easily adaptable so as to incorporate new criteria—the inclusion of social facilities situated in close proximity to existing settlements, for instance, was incorporated with the delimitation process already in motion.
In brief, the methodology, although simple, is an effective approach to buffer methods that is adequate to the scale of analysis required for small urban settlement delimitation in low-density areas.
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Landscape and Urban Planning journal homepage: www.elsevier.com/locate/landurbplan
Urban settlements delimitation in low-density areas—An application to the municipality of Tomar (Portugal) José Antunes Ferreira ∗ , Beatriz Condessa, Joana Castro e Almeida, Pedro Pinto Centre for Urban and Regional Systems (CESUR), Instituto Superior Técnico (IST), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 2 November 2009 Received in revised form 10 May 2010 Accepted 25 May 2010 Available online 6 July 2010 Keywords: Urban sprawl Land-use planning Buffer method Consolidated urban areas
a b s t r a c t One of the major issues in land-use planning is how to contain urban sprawl. To this effect, plans integrate new regulations and mechanisms that severely limit construction outside urban perimeters and restrict the areas available for expansion within the settlements. Before enforcing these restrictions, a review and correction of existing delimitation of settlements was necessary. The new limits were established through the identification of effectively consolidated urban areas. In the absence of official criteria defining them, this paper presents a methodology establishing the limits of these consolidated areas. Based on the identification, in a Geographical Information System (GIS) of existing buildings, and incorporating the analysis of road network, social facilities, and physiographic constraints (such as floodplains or steep slopes), several criteria were defined so as to delimit the urban settlements. A review of other methodologies is presented as a contextualization of the proposed one, but it is not the focus of the paper to specifically contrast or appreciate them. The study area is the municipality of Tomar, in Central Portugal, a territory with very disperse human occupation. Having achieved an accurate delimitation of the settlements’ current extent that reflects the purposes of rational land-use, the settlement delimitation was successfully revised so as to mirror the current occupation. Also, the objectivity and clarity of the adopted criteria, and its applicability to the whole municipality, allowed the methodology to be unanimously well received by the Municipal Government and Parish Councils, even if it deals with a somewhat politically delicate subject. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The publication, in 1998, of the Law for the Policy on Territorial Management and Urbanism (LBPOTU—Lei n◦ 48/98, de 11 de Agosto) established, for the first time in Portuguese Law, the general principles and goals that should steer this policy. Arising from a context of growing degradation of landscapes and natural resources, due to the scattered and unplanned occupation of vast areas, in the periphery of the main urban centres or in rural areas, the delimiting of urban perimeters rapidly became one of the main concerns for the first generation of Municipal Land-use Plans (PDM). Some of the principles stated in the LBPOTU directly address this issue, by recommending a sustainable use of the land and the weighed and sparing use of natural resources, according to the principle of economy. One of the expressed objectives of the LBPOTU is “The rational use of natural resources, the preservation of the environmental
∗ Corresponding author. Tel.: +351 218 418 305; fax: +351 218 409 884. E-mail addresses: [email protected] (J.A. Ferreira), [email protected] (B. Condessa), [email protected] (J. Castro e Almeida), [email protected] (P. Pinto). 0169-2046/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2010.05.007
balance, the humanization of the cities and the improved functionality of built-up areas”. Therefore, the human occupation of the territory should be restricted to the areas deemed as necessary for the satisfaction of housing shortages and those spaces necessary for economic activities and urban functions. Also, there should be an adequate provision of infrastructures and facilities, the main purpose being the increased equality in the access to the said infrastructures and facilities, while guarantying a minimal increase in the environmental impact. Among the objectives listed in the LBPOTU, it is stated that there should be a quest for: • “the economic sustainability of the infrastructures, avoiding unnecessary extension of both the networks and urban perimeters and promoting rational urban infill”; • “the preservation and protection of soils best suitable for agriculture or forestry, restricting the shift to other uses only when markedly necessary”. In a situation of economic and spatial restrictions, this will be reflected in the need to ensure slower expansion of urban areas, instead promoting their densification and consolidation, and limiting or prohibiting construction outside urban areas (that is, in ‘rural
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Fig. 1. The Médio Tejo Region and the municipality of Tomar.
land’). Beforehand, however, it is essential that a clear and objective identification of the continuous built-up areas, or ‘urban continua’, be made. This way, all the constructions therein will subsequently be included in revised urban perimeters, determined by the new PDM. Whenever the continua fulfil criteria related to dimension or compactness they will be recognized as consolidated urban settlements. The PDM is the instrument through which the development strategies and options stated on national and regional level plans and programmes are transferred to locally applicable regulations and land-use plans and policies, according to the Portuguese urban
law. Several PDM are currently under revision and, as with the first generation of PDM, the land-use regulations (and, specially, their consequences over building permits) on which the spatial organization of the territory is based is again assuming a front-role, attracting the highest scrutiny from both elected representatives and local population. In the revision of the PDM for the municipality of Tomar (Central Portugal, located in the Oeste and Vale do Tejo Region) it has been clearly stated that the priority should be given to the consolidation of existing settlements and the focus on housing rehabilitation instead of new construction and urban sprawl.
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Fig. 2. Current delimitation of urban perimetersand scattered construction.
It is therefore the main objective of this paper to present a methodology to delimit consolidated areas. This methodology will be applied to the municipality of Tomar within the context of the PDM revision. After the application of the present methodology, delimiting the consolidated areas, the identification of the final urban perimeters, including urban expansion areas, may be completed.
2. Study area: Tomar municipality
The municipality has a population of around 43K inhabitants. With a area of about 350 km2 , it is both one of the biggest and among the most populous municipalities in the region. The city of Tomar has a population of about 16K inhabitants. Together with its suburbs the city accounts for little less than half the total population of the municipality, whereas the second biggest settlement has just above 1K. Of the municipality’s 208 settlements, only 9 have over 500 inhabitants and 180 have less than 250 inhabitants, which gives a good measure of how scattered the population is (CESUR, 2008).
2.1. Location 2.2. The Municipal Land-Use Plan (PDM) of Tomar The objective of the current methodology is the delimitation of urban settlements in the municipality of Tomar. This municipality is located in central Portugal, in the transition between the central south-western lowlands and Tagus valley and the more mountainous central Portugal. The municipality is therefore very diverse, in terms of the relief, landscapes, and patterns of land-use. It is part of the Médio Tejo NUTS III, within the Centro NUTS II region. Set slightly to the interior of the main axis of north–south connection (the main corridor between the metropolitan areas of Lisbon and Porto), it is nevertheless located at the intersection of two important major roads (IC3 and IC9) and is served both by the main railway line and a branch line (Fig. 1).
The current PDM of Tomar, approved in 1994 (Câmara Municipal de Tomar, 1994), was produced among the first generation of Portuguese Municipal Land-Use Plans. At the time, and right after new legislation was approved, the PDM were not yet mandatory, but there was a generalized move towards their creation, on the behalf of the municipalities. This was encouraged both by special incentives being awarded to those municipalities that already had PDM (financing for infrastructures and facilities) and restrictions to the municipalities’ powers in, for instance, declaring public interest for expropriation purposes, that were thenceforth subject to the existence of a valid PDM.
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Fig. 4. Urban perimeters with unbalanced expansion areas.
Fig. 3. Examples of problems arising from the use of outdated base maps (a considerable number of dwellings already existent were not considered for the 1994s delimitation).
It is now clear that the PDM gave a major contribution towards the formation of a new cultural mind-set regarding planning issues. This process opened a window for the debate of urban planning and land-use management issues and concepts, finally creating space for consultation and negotiation in the planning process. Simultaneously, though, insufficiencies were revealed, both in the level of formation of the technicians involved and the lack of the technical data necessary for better validating the plans. Tomar was no exception and, while the first PDM was being produced, the delimiting of the urban perimeters was done resorting to very outdated geographic information and without the assurance of an adequate incorporation of suggestions made by the Juntas de Freguesia (Parishes) and private owners. As a result, several inconsistencies were identified in the present urban perimeters (Fig. 2). The municipality of Tomar presents a very scattered human occupation of the territory. The permissive development laws for ‘rural’ land, as stated by the Municipal Land-use Plan (PDM) of 1994, have in fact contributed to aggravate this form of occupation (Fig. 2). The urban perimeters delimited by the current PDM (1994) generate four complex and evidently unfair situations (Figs. 3 and 4), both towards the rights of private owners and in conflicting with the objectives stated in the LBPOTU. These factors were by no means exclusive to Tomar; much to the contrary. For one, the difficulty in coping with new legal demands was felt by most municipalities, unprepared to deal with such issues, and many Portuguese municipalities face similar problems with unsuitable urban delimitations. Also, the surge of new construction in formerly remote rural areas is an almost universal phenomenon in those areas located near the edge of large urban areas’ influence, as described in several works dealing with patterns of land-use in these rural areas under influence of urban areas—the “urban fringe” described by Bryant et al. (1982). Lewis and Maund (1976) already stated in the mid-70s that “the increasing urbanization of the countryside is a process which all advanced societies are experiencing at the present time. As a consequence the once simple and distinct division between rural and urban no longer applies”.
In the case of Tomar, the “fringe” effect is of a double nature, as the municipality itself is located at the edge of Lisbon Metropolitan Area’s influence. This contributes to a very strong push towards construction in former rural areas, as studied by Stern and Marsh (1997), Goffette-Nagot and Schmitt (1999) and Goffette-Nagot, 2000), Garreau (1991), Antrop (2000, 2004) and Lucy and Philips (1997). Even if the want of an individual landowner to build on his property is understandable, permitting it would generate both the degradation of the landscape, as is already the case with some areas of Tomar, and even issues of equal-opportunities and rights in the face of the law. Antrop (1998) reflects upon these issues, having in mind Western European examples: “Here, land is regarded as property over which the owner possesses a free right of use. The impact of individual landowners depends upon their status, reflected by the size of their property and the means to maintain or transform it. The impact of small landowners will be restricted to small areas, such as their garden or places they use for recreation. Although the effect upon the change of the global landscape might seem minimal, these small impacts must be multiplied by the large number of individual landowners. The result of this can be seen in the new landscapes”. The main consequences to Tomar’s settlement patterns were, on one hand, the heavy dispersal of construction and, on the other, the Table 1 Some rules for construction in rural classes: ‘forestry’, ‘forestry and agriculture’ and ‘agriculture’, as defined by the PDM of Tomar. Rural classes
Some construction rules
‘Forestry and Agriculture’ or ‘Forestry’
• “Construction of house for the farmer, as long as the agricultural or agro-forestal unit has an area over 2 ha and there is a contribution to the better working conditions”: minimum area for the unit – 1500 m2 ; maximum floor-area, including annexes – 300 m2 , etc. • Construction of isolated buildings for housing: minimum plot area – 3000 m2 ; maximum gross floor-area ratio – 0.05, etc. • When there are constructions within 30 m of the projected location of the new building and the plot is served by a paved road or street and basic infrastructure, the municipality may allow the building on plots smaller than 3000 m2 . • Building for housing by plot: minimum plot area – 5000 m2 ; maximum gross floor-area ratio – 0.04; maximum floor-area – 250 m2 , etc. • When there are constructions within 30 m of the projected location of the new building and the plot is served by a paved road or street and basic infrastructure, the municipality may allow the building on plots smaller than 5000 m2 .
‘Agriculture’
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Table 2 Synthesis of urban agglomerations delimitation methodologies. Methodology
Criteria and limitations
Morphological delimitation
Defined by N.U.R.E.C. 1994 (Network on Urban Research in the European Community), it takes into consideration the United Nations’ concept for contiguous built-up area, where the distance between buildings must be less than 200 m. That is, by generating a buffer of 100 m around buildings it is possible to delimit built-up continua. This sort of criteria, well suited to cities with very uniform expansion, is insufficient when these processes are a complex blend of suburbanization, sprawl and the incorporation of existing settlements. Strictly morphological criteria for the definition of a city proved insufficient in an age of stark suburbanization. Methods based on population density were then developed for the purpose of defining urban agglomerations. The delimitation methodology developed by GEMACA (Group for European Metropolitan Area Comparative Analysis) in 1996 consists in the application of 3 criteria: the economic core is the set of contiguous units with more than 7 jobs per ha and more than 20,000 jobs; the morphologic agglomeration is the set of contiguous units with more than 7 inhabitants per ha and more than 60,000 inhabitants, and the functional urban region (hinterland) is the set of units with over 10% commuting to the economic core. Cladera (2003) presents a number of applications that resort to this methodology. One of the first was that of the Census Bureau of the United States of America, from 1950, and is still the basis for the definition of Metropolitan Areas in that country. Then, the criterion used was that of aggregating all counties with at least 2/3 of the active population working in non-agrarian functions. In 1959 the Institute of International Research defined a metropolitan area as containing both a central city, or nucleus, with over 50K inhabitants and the contiguous administrative units that had a fraction of non-agrarian jobs above 2/3. The total population should be above 100K. In 1970, Cafiero et al. defined the metropolitan area as having more than 100K inhabitants, 35K or more non-agrarian workers and a job density for non-agrarian functions of 100 jobs/km2 . McDonald (1987) presents another methodology of this type, focusing on the identification of urban employment subcentres. Involves the analysis of commuter flows (home/work place) and economic and social criteria. The COMET internet site presents the criteria developed by the IinterregIIC-project ‘Group for European Metropolitan Areas Comparative Analysis’ (GEMACA II). In this project 14 Functional Urban Regions in North-Western Europe were analysed by using a delimitation according to economic core of metropolitan area (sets of contiguous units with more than 7 jobs per ha and more that 20,000 jobs), hinterland (set of units with 10% or more commuting to economic core), population (total population >1 million) and cores (monocentric and polycentric cores are possible).
Demographic delimitation
Delimitation based on the economic and social structure
Functional delimitation
deficient consolidation of the planned expansions, caused by the rapid and unplanned manner through which these were created (Fig. 2). The current regulation, contained in the PDM, may have worsened the scattered construction, by allowing construction in land classified as rural. (see, for example, the articles 28 and 29 of the PDM specified in Table 1). Thus, building is basically allowed in a plot located in spaces destined for agriculture or forestry agriculture whenever the area exceeds 3000 m2 . In this case (and most plots in Tomar will fulfil the criteria), the building of a house with a floor-area of 150 m2 is easy. The mentioned rules, coupled with the existence of a strong pressure for construction of some housing types, generated a strong
surge in the number of requests for building permits outside urban perimeters. The dominating typologies are the detached singlefamily housing, both in the close vicinity of urban settlements or on the outskirts of the city of Tomar, and the isolated singlefamily house, aimed for the weekend- or summer-house market. The parishes of Tomar in which this weekend- or summer-house typology assumes greater importance are precisely those that are farther from the city. In the meetings held with the parish councils, as part of the consultation procedures of the PDM’s revision, it was gathered that this second-house belonged mostly to individuals that had their roots in the area but lived and worked outside the municipality (that is, emigrants, but of local origin). On the other hand, those new houses located near the reservoir of the Castelo de Bode Dam were mostly destined for ‘outsiders’, not originally from the area. The lack of an adequate supply of building plots within urban perimeters or the difficulty in acquiring them from landowners unwilling to either build on them or sell them to those who will, may have contributed to the strong building pressure outside urban settlements. The slim supply of housing in the city of Tomar and the slow or stalled rate of conclusion of some large-scale urban plotting and urban plans situated inside the city’s boundaries were also indentified as probable causes for this sprawl. The need to update and extensively revise the urban perimeters, adjusting them to the present reality of the municipality became, as well as evident, essential to the subsequent stages of the PDM revision. 2.3. The Regional Plan for the Oeste e Vale do Tejo (PROT-OVT) During the current revision of Tomar’s PDM, the intention to strengthen and consolidate existing settlements has been repeatedly stated, instead of the definition of over-dimensioned expansion areas and construction in “rural” land, avoiding, whenever possible, the linear extension along the roads. This is, in fact, one of the main concerns of the Regional Plan for the Oeste e Vale do Tejo (PROT-OVT), a planning instrument of higher hierarchy, to which the PDM must conform. Two of the planning principles stated by the PROT-OVT (CCDRLVT, 2008) are: • Concentration of constructions: The PDM should establish models for land-use that promote the concentration of construction in urban settlements or rural clusters, adequately identified and delimited for this purpose. This should serve as to avoid all forms of scattered and linear expansion and excessive extension of the settlements, pursuing instead the reconversion, restructuring or rehabilitation of existing built-up areas, already served by infrastructures and facilities; • Contention, proportionality and programming of urban areas: The PDM should dimension and program the structuring and consolidation of urban land in accordance with the real needs, current and projected, taking into account different types of demand for housing, economic activities and other urban functions. The PROT-OVT also identifies a set of norms for the identification of new urban areas or the creation of expansion areas for existing settlements, along with criteria for classifying land as urban instead of rural. A ‘consolidated urban area’ is a cluster of at least 80 buildings for housing or other urban uses, in continua that have a building density of at least 7 buildings per hectare. As for the different classes of rural land, the PROT-OVT warns against the widespread permission of single-family houses’ construction in isolated plots. It recommends instead their concentration in low-density settlements and rural clusters that follow the dominant traditional patterns of rural communities, as well as
J.A. Ferreira et al. / Landscape and Urban Planning 97 (2010) 156–167 Table 3 Urban settlements delimitation. Country and references
Criteria
Netherlands (Statistics Netherlands) Leeuwen (2006, 2007)
Population cluster map: morphological delineated area; mainly groups of residential houses; recognizable street pattern (no ribbon development); form one cluster when: separated by less than 200 m (>200 m when connected by bridge); minimum number of dwellings.
Grid method: • total number of dwellings per grid (dwellings from housing register with addresses; addresses provided with coordinates); • proximity factor (each cell calculated a proximity factor).
Finland (Statistics Finland) Kanerva (2001)
Localities are clusters of buildings housing at least 200 residents, where the distance between buildings normally does not exceed 200 m. It takes into account buildings other than residential buildings, i.e. buildings used exclusively for work places. However, it does not include buildings used for agricultural production. Hospitals and other institutions situated outside localities are included only if the number of their resident staffs, including family members, is at least 200 (hospital patients are not taken into account). The method creates a grid where cells that hold residential buildings are selected. These are aggregated whenever contiguous and converted to polygons. A buffer is generated, with a distance based on the number of residential and non-residential buildings contained in the cluster of built-up cells to ensure all buildings are fully included. Buffering merges the adjacent polygons together if they are closer than two times the value of distance from one another.
Step 1: Buildings, grid and buffered grid polygons: “urban” cells within the grid are selected, based on them containing a given number of dwellings. Contiguous “urban” cells were merged together, forming clusters defined by polygons.
Step 2: Selecting building blocks inside the area of influence of a locality: areas with 200 people were picked out. To find building blocs in close contact with a locality, a buffer zone was formed and the polygons inside or touching the buffer line were picked out.
Step 3: Merging polygons together by buffering: The polygons were merged to the main area by buffering.
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Table 3 (Continued ) Country and references
Criteria
Step 4: Resizing buffer zone back to original: To obtain the final form of the locality, the buffer zone was resized back to its original dimension.
Norway (Statistics Norway) Dysterud (1999)
An urban settlement in Norway is defined as an agglomeration having at least 200 residents, and where the distance between the houses – as a rule – does not exceed 50 m.
promoting the reuse of derelict housing and rehabilitation of the existing housing. An exception is made to real working farms, but with a much narrower understanding of what the minimal area for the farm should be. The enforcement of the regulations stated by the PROT-OVT does therefore strengthen the need to better define the urban continua.
3. Methodology for the delimitation of urban settlements 3.1. Existing methodologies A set of methodologies is used by several authors (Ferrão et al., 2002; Cladera, 2003; Ramos and Silva, 2007) for the delimitation of urban agglomerations, as systematized in Table 2. These are organized into four main types of delimitation methodologies that address slightly different aspects or constraints in base-information by using very different criteria for segregating or merging areas so as to generate the urban agglomeration. It is not the purpose of the following to discuss the overall merits of each methodology, but simply to provide a brief overview. This aims at synthetically analysing what alternative methodologies are there, and whether they are appropriate to low-density urban settlement delimitation in Tomar’s context. By incorporating, among other criteria, concentrations of employment and economic influence defined by commuting, these methodologies are not adequate for small urban settlement delimitation. Most settlements under analysis have only about 80–250 inhabitants, with residual urban economic activity. Nevertheless, some of the concepts aforementioned can be, and were, explored in defining the methodology for small settlement delimitation—concepts such as the definition of population thresholds, or the identification of the average distance between buildings in urban context, by way of buffer generation, as used in morphological delimitation. Satellite images are fast becoming a good instrument for the delimitation of agglomeration areas but arguably not for the scale of analysis required for these very small settlements located in areas of scattered construction. The remote sensing or digital processing of satellite images is indeed used in defining metropolitan agglom-
erations in various works, such as Bosselmann (2008), Donnay et al. (2001) or Mesev (2003), but focusing on large metropolitan areas delimitation and comparison or segregation of urban land-use at a large scale. Until recently, the resolution was also insufficient for detailed urban delimitation, as noted by Pauleit and Duhme (2000). With the spectacular improvement in the spatial resolution of commercially available satellite imagery, it is perfectly conceivable the substitution of aerial photos in the very near future. There is, nevertheless, a traditional reliance on rectified aerial photography, that has led most municipalities to acquire and regularly renew this base-information at affordable costs. This was the case with Tomar, where this type of imagery had been acquired recently and therefore was made the obvious choice for settlement delimitation. Much in the same way, the methodology that combines Synthetic Aperture Radar (SAR) and optical data for urban mapping, developed by Corbane et al. (2008), proved inadequate to the scale and financial constraints of local planning. The more traditional digital processing over aerial photography, as referenced for instance in Webster and Beckett (1970) or Falkner and Morgan (2002), was therefore both the more economical and practical solution. Given the choice of orthorectified aerial photography as the source of imagery, the methodology would have to be adjusted to the available sources of digital data, and specifically to the analysis of the existing buildings and their clusters. Closer to the local scale that is required for Tomar, a few methodologies were analysed, developed by statistics agencies from Finland, the Netherlands and Norway (Table 3), that address comparable issues. These methodologies adopted by the statistics offices are very similar to the methodology presented in this paper, both in scope and in the steps taken to achieve the delimitation of settlements (define clusters of housing and then merge, through buffering, all clusters within a given distance of each other). Nevertheless, they fail to address (as it was not the purpose of the statistics offices’) issues strictly related to spatial planning, such as: the inclusion of the aforementioned morphologic constraints to building (e.g. slopes, floodplains); the protection of natural resources (e.g. riverbeds, protected land); whether or not the areas were served by the road network; or if social facilities were to be aggregated to the settlements.
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Table 4 Methodology steps.
1st Step
Previous condition: Generate a buffer of 25 m around each existing building and identify clusters of buildings (whenever the buffers meet) → only clusters with over 25 buildings in continuum are considered as ‘consolidated areas’. The 25 m used in generating the buffers were the result of an analysis done over digital maps and crossed with on-site observation of the building patterns in rural Tomar. Several other buffer distances were iterated but 25 m buffers (a distance below 50 m between two buildings) were those that more closely reflected the observed continua and breaks. The 25-building clusters correspond to an adaptation of the rules contained in the PROT-OVT.
2nd Step
Identify urban streets: All roads located within the cluster defined in the previous step.
3rd Step
Generate a buffer of 50 m around the urban streets. This will define the basic limit for the ‘consolidated area’. The following steps define exceptions that may alter this first limit.
4th Step
Whenever there is a gap of at least 70 m without any building on one of the sides of the street, the limit is pushed back to the street. These 70 m correspond to the sum of the 25 m buffers along the road, from each of the bordering buildings, and the 20 m gap that is considered to be the threshold for a continuum to exist.
5th Step
When there are non-built-up areas located within the limit that qualify as REN (floodplains or slopes with an incline of over 25%) or RAN, the limit will exclude any area located over 6 m away from existing buildings—just enough to guarantee some minor imprecision on the maps will not carry legal consequences over building rights for existing houses.
6th Step
Whenever two clusters are located no more than 20 m apart, they may be merged, whenever there is not the need to guarantee the safeguard of ecological corridors or the limiting of over-long linear development.
7th Step
Include within the limit buildings that were part of the original (1994) urban perimeter, maintaining their status as “urban” constructions. In these cases, the limit is drawn so as to include the building and a buffer of around 6 m, linking it to the limit defined by the previous steps.
8th Step
Whenever a public facility is located within a 50 m distance to the previous limit, the latter will be extended so as to include the facility within the ‘consolidated area’. The 50 m are the result of adding to the 25 m buffer to the last building in the settlement a 50 m walking distance to the facility.
Another methodology reviewed is that described by Valentim (2007), based on spatial statistics (grid method), for the identification of clusters with more than a certain threshold of discrete elements located in contiguous locations (e.g. houses), by identifying local densities for each cell with the grid.
This methodology was also used in the context of settlement identification in the municipality of Tomar, but analysed only the urban and suburban areas of the city, and not the smaller rural settlements, thus requiring adaptation. Even so, the methodology is very similar to the one hereby describe, except for the criteria
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adopted (such as buffer distances and the inclusion of new spatial planning criteria), and in that the present methodology waves a fully automated spatial statistics methodology. The adoption of this semi-automatic application of the chosen criteria became obvious due to the unavailability of sufficiently accurate digital information for some of the more relevant aspects of spatial planning. Among these, were such items as the geomorphologic constraints or the existence of social facilities near a settlement, which it would render a fully automated application exceedingly complex. 3.2. Proposed methodology for the identification of consolidated areas 3.2.1. Input data The methodology developed in part around the existing sources and current municipality’s databases, so as to minimize the costs involved and to allow for a quicker incorporation of updates. Upfront, the most detailed image of existing construction, and the one that is constantly being updated by the municipality’s urban planning services (Departamento de Planeamento Físico) is a digital database, based on the vectorization of rectified aerial photographs. This digitalization is done on ArcView GIS software (©ESRI) roughly every year, based on the availability of new aerial surveys. The latest version is based on aerial photos dating back to 2007, which provide the best information possible on the current situation. Most other relevant information used as a basis for the delimitation is also provided in ArcGIS formats (shape files and databases), and this was also the software used in implementing the methodology described hereafter. Some other relevant information provided both by the municipality’s services and by government institutions, was also provided mostly as shape files or other ArcGIS file formats. These include the Digital Terrain Model and relief map with contour lines at 5m intervals; base-information for the Ecological National Reserve (REN), including steep slopes and floodplains, and the Agricultural National Reserve (RAN); shape files with streams, reservoirs and social facilities; and the 1994 cartography from the original PDM. All digital data was projected on one of the official projection systems for Portugal, the Datum 73 IPCC Hayford-Gauss. The final output is expected to comply to only a 1:25,000-scale detail, but the present delimitation is obviously unmanageable at such a scale, given the minute size of most of the elements under analysis—a much more detailed analysis is therefore required. A precision of around 1.5–2 m is achievable using the software and base data available, even though the required accuracy for the final output maps will be of only 12.5 m. Nevertheless, this enhanced precision will be helpful for other applications of the obtained results, such as day-to-day land-use planning and analysis of requests for building permits by the municipal services. 3.2.2. Method steps To best characterize the current structure of settlement of the municipality of Tomar, a methodology was developed for delimiting precisely today’s extents of the consolidated areas of each urban area. This is paramount to the definition of the ‘rural’ or ‘urban’ classification of the land. The objectivity, universality and transparency of the methodology were deemed as crucial and the defined criteria led to following steps (Table 4): The first 3 steps define the polygon within which the urban continuum is enclosed. Steps 4-through-8 allow for the incorporation in the methodology of essential exceptions. The 5th step, for instance, concerns the protection of natural continua and corridors. The capability of identifying and removing the more environmentally sensitive areas from the urban perimeters will prove fundamental to the subsequent definition of the municipal eco-
logical network. This network’s definition is an integral part of the PDM’s revision, and the need to protect the corridors therein is sustained, among many others, by Fedorowick (1993) or Ahern (1991). 3.3. Results The results produced by applying the methodology, defining the consolidated urban areas and the comparison between these and the perimeters for the Urban Settlements as defined by the 1994 PDM are presented in Fig. 5, with the indication of areas that superimpose between both delimitations and those that differ: areas pertaining to the 1994 limits that were identified as not being part of a consolidated area and those that were not part of 1994 urban perimeters but are currently consolidated urban areas. It should be emphasized that the consolidated urban areas closely reflect the de facto settlement of the municipality, obtained through the analysis of existing buildings and settlements. In fact, even though the methodology was, at first, developed without having the criteria contained on the PROT-OVT, still unavailable at the time, the methodology proved to closely conform to them with resource to minimal adaptation, which seems to confirm its adequacy to the principles that guided the PROT-OVT and the criteria therein. Some key results of the methodology’s application to the municipality of Tomar are presented in Table 5. Although one of the main preoccupations during the inception stages of the methodology was that, by recognizing pre-existent settlements or houses just outside the 1994 perimeters a significant increase in the total urban area might occur, the results were, somewhat surprisingly, quite the opposite. Although the number of settlements increased from 197 to 208 – by rectifying situations where urban continua were beforehand ignored – the total urban area did not. In fact, it was significantly reduced, by almost one-quarter. Despite the reduction in total urban area, the number of buildings encompassed by the new limits increased from around 30,000 to almost 37,500. This means 77.4% of all the buildings fall within the consolidated urban settlements, as opposed to only around 62% with the previous delimitation. The proposed methodology and the results produced by its application to the municipality of Tomar were presented to the municipal council, the Regional Development Coordinating Commission (CCDR-LVT) and the 16 parish councils, in a series of meetings held between July and September 2008. The several representatives had a positive reaction both to the methodology and the results obtained. It was also stated the need for a second iteration of the methodology after the incorporation of updated geographical information, concerning buildings constructed after 2004, which may change a few details in the delimitation of some consolidated areas. These should produce but small alterations, according to a preliminary analysis done with the assistance of municipality’s services and Parish Councils. Nevertheless, by having resorted to GIS technology, the process of delimiting was both much more efficient and quick than traditional methods but will also allow for a simple updating of the results, when new information becomes available. The determination of some of the values, such as the distance between buildings or the averaged depth of the plots, was subject to an iterative process, taking into consideration the distinct characteristics of the different areas of the municipality of Tomar, and proved adequate for the delimitation of the consolidated areas, closely reflecting the concerns and complaints made by the parish councils in relation to the 1994 delimitation. The evident effort made to eliminate all subjective criteria and to closely fit the methodology to the reality verified in the munic-
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Fig. 5. Comparison between consolidated urban areas (2008) and urban perimeters as defined by the PDM (1994).
Table 5 Comparison between the delimitation of urban settlements by the 1994 PDM and the application of the present methodology.
Number Total area (ha) Buildings Number % of Total
Urban Settlements delimited in the 1994 PDM
Consolidated urban settlements
197 3.844
208 2.906
30.390 62.7
37.489 77.4
ipality ended up mostly coinciding with the confirmation and correction of several unjust situation or errors in the previous delimitation and already identified both by the parish and municipal councils. As such, and since the subjectivity of previous efforts was eliminated, the methodology was unanimously accept by these political bodies. 4. Discussion and conclusions The main driving force behind the proposed methodology was the need to correct the errors detected in the previous delimita-
tion done in the 1994 Municipal Land-Use Plan (PDM) of Tomar. The limits drawn by that PDM brought about evident injustice: the exclusion of houses located right next to urban settlements’ limits, and the virtual unavailability of plots for new construction within the boundaries of some historically important settlements, were readily identified as critical issues that needed to be addressed by the PDM’s revision. The proposed methodology intended to obtain maximum acceptance, both by the municipal council, municipal assembly and the parish councils, while simultaneously reflecting the Regional Plan guidelines that stress the need to contain scattered construction and urban sprawl and to consolidate the urban system. Having finally achieved an accurate delimitation of the urban settlements’ current extent, it will then be possible to establish expansion areas that directly reflect the purposes of rational land-use, in accordance with the LBPOTU. The priority will be given to the consolidation of the existing urban structure, namely through the identification of a clear urban system hierarchy. Therefore, it will be possible to enforce or reinforce clusters of public facilities and services that may, along-side an enhanced public transport system, allow for a better coverage of the demand in
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remote rural areas of the municipality. This will also permit a more rational use of limited public funding. The methodology had very precise targets and budgetary constraints in mind, but this was by no means a limitation to its overall coherence and pertinence to the land-use analysis that was its main objective. Reviewing other methodologies proved useful, but none fulfilled the necessary criteria. To give an example, the buffer method used by the Norwegian Statistics Office, presented earlier, is very similar to the present one, but does not, for instance, encompass situations where social facilities are in close proximity to a settlement. In all the methodologies analysed, some very relevant issues pertaining to the field of spatial planning, such as the incorporation of physiographic constraints (e.g. slopes, floodplains) were not considered—due to the mainly statistical nature of most methods. It was also evident, even beforehand, the inevitability of migrating the delimitation process from the traditional analogical methods, over printed maps, to a semi- or fully automated method. The advantages of GIS use in contexts of shifting land-uses, especially in urban areas or rural areas under urban influence is well documented, in such works as Holden and Turner (1997), Dai et al. (2001), Li (2004) or Lópeza et al. (2001). The need to include this level of analysis in the criteria for the settlements’ delimitation led to a semi-automatic approach, as some of the data was virtually impossible to analyse in a fully digital process. Some of the more significant limitations of the methodology are: • the need to constantly update the main GIS database with new information, such as new buildings or shifts in land-use; • the possibility that a given new building may generate new spatial relations between different clusters – suggesting the merging of two settlements – may be difficult to cope with bureaucratically and cause significant shifts in the total urban area of a given parish; • even though information on the specific function of each of the buildings’ polygons was available (e.g. housing, warehouses, industries, etc.), the reliability of the information was insufficient for this typological classification to be incorporated into the criteria. Nevertheless, in case there is a scrutiny of the data that will ensure its accuracy, new criteria may be added effortlessly into the methodology, such as the separate analysis of industrial and residential clusters, or the identification of commercial centres. The methodology includes some innovations and adaptations, in relation to the other reviewed methodologies: • the simple and straight-forward approach towards data analysis, tailor-made to suit the ready-available base-information, while maintaining the preciseness of the results and technical standards intact; • the objective being the determination of “net” urban areas, all major urban voids within the settlements are excluded, thus defining more accurately the effectively built-up areas, unlike the methodologies adopted by the statistical offices; • the methodology includes steps that analyse, and allow for the exclusion of, physiographic constraints, such as steep slopes, best agricultural soils or floodplains; • the base-information, being essentially all available from the municipality’s services and government institutions, is inexpensive; • it is easily adaptable so as to incorporate new criteria—the inclusion of social facilities situated in close proximity to existing settlements, for instance, was incorporated with the delimitation process already in motion.
In brief, the methodology, although simple, is an effective approach to buffer methods that is adequate to the scale of analysis required for small urban settlement delimitation in low-density areas.
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