Standards for digital topographic data: The Canadian experience

019%9715/84 $3.00+0.00 Pergamon Press Ltd

STANDARDS FOR DIGITAL TOPOGRAPHIC THE CANADIAN EXPERIENCET

DAT_4:

J. M. ZARZYCKI Director

of Topographical

Survey Division, Surveys and Mapping Branch, Department and Resources. Ottawa, Ontario KlA 0E9, Canada

of Energy.

Mines

Abstract-Proliferation of digital topographic data collected at different levels of governments, utility and private sector necessitates establishment of National Standards so that these terrain data can be exchanged, to everyone’s benefit. Under the auspices of the Canada Council on Surveys and Mapping and in co-operation with a wide spectrum of producers and users of digital terrain information, a set of National Standards for the Exchange of Digital Topographic Data was developed. These standards cover the classification (taxonomy) of topographic features, standards for quality evaluation and EDP standards.

INTRODUCTION

Digital mapping and computer assisted cartography are today recognized as integral parts of mapping activities at every level of responsibility, be it the basic national topographic mapping, detailed engineering maps of urban areas, cadastral and land information systems, utility digital data bases or communication, hydro or other engineering projects needing terrain information. Rapid advancements in digital technology and computer graphics have put at the disposal of map makers several powerful tools for the acquisition of terrain data in digital form, management of digital data bases and semi-automated production of graphics by means of computer assisted methods. The problem today is not lack of acceptance of digital terrain information systems (although not everyone as yet fully appreciates their potential and challenge), but the lack of a common standard which could aid organizations entering the digital mapping field in setting up their systems and provide a basis for the exchange of digital terrain data, to everyone’s benefit. Relatively easy access to a growing number of digitizing instruments has created a proliferation of digital data collected at different levels of government, utilities, and private companies, without much thought having been given to a common standard which would facilitate exchange of digital data. Ideally, the same topographical feature, whatever it be, a road, house, property boundary or a telephone line, should be digitized only once by whatever organization has the first need for these data and from the best source. It should then be supplied to other users. I realize that such an ideal situation will not exist, despite best efforts on everyone’s part. However, I believe that in the digital era, duplication of effort can be substantially reduced if there is good will on the part of all concerned. A uniform digital data base which would satisfy the needs of all organizations is not feasible, nor is it required in order to achieve the objective of exchanging digital terrain data. What is needed, however, is a National Standard for the Exchange of Digital Terrain Data which will facilitate communication between distributed data bases. In the opening paragraph, I mentioned both digital mapping and computer ussistrd curtogruphy. These are two separate but related activities, and it is important that the distinction between them is fully understood so that we can develop and formulate new concepts which are applicable to the digital era. Digital mapping is a system for collecting, classifying, storing, retrieving and managing of terrain data in digital form in a manner that is not tied specifically to a single application and that facilitates the use of this digital data for a multitude of applications. The result of digital mapping is a “Digital Map”-a digital topographic or thematic data base (not a graphic) from which data can be retrieved selectively in an orderly manner, brought into tThis paper was presented as part of the Land Records Track of the 1983 AWIW/ Corlf~~cr ~f‘L’RI.SA. in Atlanta. Georgia. It has since been published in Surce~~irq md Muppinq 44/l (March 1984). and is included in this issue with the aggreement of the Journals Editor of the American Congress on Surveying and Mapping. Falls Church. VA. 209

210

J. M. ZARZYCKI

association to fulfil user’s requirements as input to user’s mathematical models for analysis, or employed to create cartographic files for production of a multitude of graphics by computer assisted methods. This “Digital Map” has no scale in the traditional sense; therefore the criteria of accuracy and content associated with map scale must be replaced by new concepts which are applicable to the “Digital Map”. Computer Assisted Cartography on the other hand is a system for producing graphics from the data contained in the “Digital Map” by means of computer assisted cartographic methods employing proper symbolization to provide a clear and pleasing visual representation of the terrain.

DEVELOPMENT

OF

STANDARDS TOPOGRAPHIC

FOR

EXCHANGE

OF

DIGITAL

DATA

In order to exchange data between “Digital Maps” (Digital Topographic Data Bases) compiled by different levels ofgovernment, utilities and resonrce companies it is imperative that an agreement is reached on a minimum set of standards which is acceptable to the majority of producers and users of digital terrain data. In Canada the principal mapping activities are undertaken on federal, provincial and municipal levels. In addition oil companies, utilities such as Hydro Quebec, telephone and pipe line companies are entering the digital mapping field. The development of a Digital Topographic Data Base started in the late sixties at the Surveys and Mapping Branch of the Department of Energy, Mines and Resources (EMRtthe national mapping agency of Canada. Shortly thereafter the provinces and municipalities as well as the private sector entered the digital mapping field. It was recognized from the beginning that the digital mapping environment offers many opportunities for elimination of duplication of effort and for rapid up-dating of digital data bases as well as of the graphical products. As the digital mapping technology gained increasing acceptance in Canada, the Canadian mapping community searched for ways to ensure that maximum benefits could flow from this new technology. The Canadian Council on Surveying and Mapping (CCSM), a body composed of the directors of federal and provincial mapping agencies, examined the digital concepts and activities in Canada and became concerned at the lack of standardization and the wasteful duplication of efforts in digital mapping. In October of 1978 the CCSM passed a resolution asking the Surveys and Mapping Branch of EMR to create appropriate mechanisms for the formulation of standards for digital mapping including the storage and retrieval of digital map data, involving federal, provincial and municipal governments, the universities and private sector. The author was charged with implementation of this resolution. Two months later in December of 1978 a planning meeting took place to establish guiding principles and terms of reference for technical committees. This planning meeting was attended by representatives from each province, the federal mapping agencies, the Canada Petroleum Association and the Canadian Association of Aerial Surveyors. It was recognized that standards for digital mapping cannot be imposed from above and that the best way was to assure their wide acceptance and use is to involve a large spectrum of producers and users of digital data in the process of adopting them. This however posed some practical problems when it came to the composition of technical committees. Large technical committees could become a forum for interesting and lengthy discussions but would be ineffective in terms of producing meaningful results within a reasonable time frame. For this reason it was decided to limit the membership of each technical committee to approximately 10 persons. However, in order to get input from organizations not represented on all of the technical committees, several members of each committee were asked to solicit views from outside organizations and to bring these views to their technical committee meetings. For example, members from provincial survey departments were tasked to represent the interests of municipalities. The planning meeting held on December 4, 1978, established a technical committee on each of the following: (I) A standard classification (taxonomy) of topographic features. (II) Standards for the quality evaluation of digital topographic data. (III) An EDP standard for digital topographic data.

Standards

The whose and to The

for digital

topographic

data

211

Topographic Survey Division of Surveys and Mapping Branch provided the Secretariat, function was to support the activities of technical committees, to coordinate their activities produce reports. terms of reference for each of the above technical committees were as follows:

Technical Committee I In general terms the task of this Committee was to develop and recommend the adoption of a uniform classification system for topographic features for the exchange of digital topographic data. More specifically, this Committee was charged to: (1) Examine existing classifications of topographic features based on federal, provincial and municipal mapping specifications as well as on practices of related disciplines such as geography, forestry, pedology, land use, real estate law, etc. (2) Investigate the feasibility and practicability of a single uniform and national classification system for topographic features, universally applicable regardless of the scale of graphical representation. (3) Based on (1) and (2), recommend(a) a single national and uniform classification system for topographic features, scaleindependent and suitable for the exchange of digital data, or alternatively: (b) a uniform classification system consisting of sub-systems properly integrated to form a national system for the classification of topographic features and suitable for the exchange of digital data. Either alternative will include the preparation of a dictionary of terms that can be used to describe clearly and unambiguously all topographic features. (4) Develop a coding system for the adopted classification system of topographic features. Technical Committee II The task of this Technical Committee has been to develop standards for the resolution and accuracy of digital topographic data. The Committee is also to recommend standards for rating the up-to-dateness and completeness of digital topographic data. More specifically, Committee II was charged to recommend a set of rules by which producers of digital topographic data will be enabled to calculate realistic estimates of the accuracy of the data contained in their files. Technical Committee III In general terms the task of this Technical Committee has been to develop standards for application of EDP technology to digital topographic data. More specifically, the Committee was charged to : (i) Develop standards for the transfer of digital topographic data on various media such as magnetic tapes and disks, and punched cards. These standards concern the physical characteristics of data elements, labelling and file structure. The committee is making maximum use of standards available for other types of data. (ii) Develop standards or conventions for the logical definition and organization of all topographic data elements. These are concerned with the various ways of representing topographic features in digital form as well as the logical arrangement of the data. SOME Use

GUIDING

PRINCIPLES

BEHIND

THE

STANDARDS

qf the classijication standard

The proposed classification standard is not intended to be imposed upon all potential users. It is realized that there are many existing systems that have been successfully developed and implemented to meet user’s specific applications and that will continue to be used. It is also acknowledged that such special purpose systems may be developed and implemented in the future. It is hoped, however, that the proposed standard will be sufficiently general and flexible to accommodate the exchange of digital data while still accommodating any user wishing to convert

J. M. ZARZYCKI

212

to them. The main advantage of conversion to the standard classijkation system will be the facilitation of data exchange. Although it is not necessary that all systems, whether existing or new, should be obliged to operate on the proposed classification standard, each must be able to “map” into the standard in order to be able to exchange digital data with others. Figure 1 illustrates this concept.

r-l

User 0

operoting

on standard

Translator software (A)

h

/

Translator software IDI

Fig. I. The use of a classification

standard

In Fig. 1, User A is operating two different systems that are not structured in accordance with the classification standard. Users B and C are operating systems that are structured on the standard. User D is operating a system that is not structured in accordance with the standard, but is also different from User A. In order to receive data from any other user, or send data to any other user, User A must first “map” its own classification into the standard via a specially written “translator” software program. Users B and C could exchange data directly with anyone who also is on the standard. User D, like User A must use a translator program before being able to exchange data. Concepts of classijcation Technical Committee I has favored a classification structure that can accommodate new features and feature-attributes. The map making community includes thematic map makers as well as topographic map makers. The classification standard must provide for production and exchange of thematic as well as digital topographic data. Of course, only those features of the thematic digital data which also appear in the topographic digital data can be translated.

Standards

for digital topographic

213

data

The “translated” data can be grouped by processing. Practical tests would be undertaken to establish a satisfactory procedure. It may also prove advisable to add features from the thematic field as entities in the digital topographic data classification system, although they may not be topographic features in the true sense (for example, centroids of enumeration areas or parcels). The digital thtmatic system will then be translatable into the digital topographic system via the standard, and vice versa. The adoption of the standard classifications of the digital topographic system by the thematic user will then be feasible. As the work of this Committee progressed it became more and more apparent that it was feasible to have a scale-independent classification system. This approach is likely to simplify interdepartmental topographical data exchange between federal, provincial and municipal levels of government. It will also simplify the federal-provincial and provincial-municipal exchange. For the classification of topographic features, Technical Committee I adopted the “tree structure” approach. Topographic features were classified into 10 major classes (Level I). Each class is subdivided into several categories (Level II). Under each category the features are listed in Level III, and the feature attributes are given Level IV. The following are examples drawn from this classification scheme: Level I (Class) Designated

area

Agncultural

FarIll

Commercial

Feed lot Shopping Yard

structure

AgrlCUltUK4

Roadway

Roadway

or Railway

Level IV (Attributes)

Level III (Feature)

Level II (Category)

Dairy, Poultry etc. centre complex

Corn cnb Feeder station Silo Stock pen Wind pump Road (gravel divided)

etc.

Coal Junk Lumber

I lane each way 2 lanes each way 3 lanes each way

The following coding of topographic features was adopted: -use of letters A-Z for classes in Level I -use of letters A-Z for categories in Level II -use of a 5-digit number for features in Level III -use of a 3-digit number for attributes in Level IV This can be illustrated on the following examples: BARREN LAND JE 01550 000 BARREN LAND-GRAVEL JE 01550 110 BARREN LAND-ROCK JE 01550 120 BARREN LAND-SAND JE 01550 130 BARREN LAND-SILT JE 01550 140 J E 01550 110 120 130 140

is the is the is the is the is the is the is the

Standards&w

code code code code code code code

for for for for for for for

“Land Cover” in Level I. “No Vegetation” in Level II. feature “Barren Land” in Level III. attribute “Gravel” in Level IV. attribute “Rock” in Level IV. attribute “Sand” in Level IV. attribute “Silt” in Level IV.

quality evaluation

The development of standards for quality evaluation of digital topographic data became more involved than was originally envisaged. In the graphic environment the concepts of accuracy and

214

J. M.

ZARZYCKI

content can be easily associated with the scale of a map. This is not the case in the digital environment. Terms such as accuracy, precision, resolution and completeness had to be clearly defined before they could be applied in the standard and must be conveyed to the user of the digital data in an orderly and systematic manner. The factors affecting these terms were examined in order to establish procedures for the evaluation. To develop standards for quality evaluation of digital topographic data, Technical Committee II conducted an in-depth study of the digital mapping process, e.g. project planning, control, aerial photography, aerial triangulation, stereocompilation, cartographic process, digitization, etc. As a result of this, the Committee developed a practical method to achieve the desired evaluation parameters and also included in the report the appropriate equations for the theoretical evaluation of the accuracy parameters. To ensure proper management of digital topographic data, the Committee selected several parameters to be defined by the producer of these data, e.g. map or area identifier, coordinate system and units, projection, spheroid, datum, number of overlays and future classes, accuracy, up-to-dateness indicator, etc. The report of this Committee also includes a comprehensive review of existing accuracy standards in use in Canada and major mapping organizations. A review of existing methods and equipment for data collection also is given. EDP standards

The EDP standard has been developed to provide a national format for the exchange of topographic data on magnetic tape taking full cognizance of all relevant standards and in particular the standards for Computer Compatible Tape (CCT) formats as established by the Landsat Ground Station Operators Working group (LGSOW) and Configuration Control Board (CCB). As a medium for the exchange of the digital topographic data, Technical Committee III preferred the use of 9-track, 1600 bpi, 2500 ft magnetic tape with no industry standard label on it. Upon reviewing the existing EDP standards, this Committee focussed on the CCT data structure developed by the LGSOWG and CCB. This format is called “Superstructure” and uses three selfdefining records, namely, the File Descriptor Record (FDR), File Printer Record (FPR) and the data record(s). Of interest here is the data record(s) which forms the Topographic Data File Set (TDFS). This TDFS consists of a Master Header File (MHF) and Topographic Feature File (TFF). The MHF describes the topographic data in terms of: precision, resolution, accuracy, completeness, up-to-dateness, identification, graphic location, etc. The TFF contains the following data records: -Feature Attribute Group (FAG) -Segment Attribute Group (SAG) -Coordinate Group (CG) The EDP standard allows for the assignment of attributes for a feature and a segment of this feature. In each group, there is a minimum set of attributes, e.g. in the FAG, we find the “future coordinates”, etc., while in the SAG we find “data type” to indicate whether code”, “min-max the feature is point/line/curve/geometrical figure/etc., in terms ofclosed/open/feature to right/feature to left/etc. The CGs consist of a variable number of units, where each unit contains a Coordinate triplet (x, y, z).

CURRENT

STATUS

Since the draft of the proposed standards for digital topographic data was printed in April 1982 approximately 700 copies have been distributed to various federal, provincial and municipal government departments, private industry and universities in Canada and to 22 other countries. Recipients of the draft have been asked for critical and constructive comments. Some 200 replies have been received, of which about 40 included quite detailed evaluation. These are very valuable comments which will help to develop better national standards. The secretariat under the direction of Dr M. Allam studied all replies, catalogued them, and submitted them to the appropriate technical committee(s) for consideration. The technical committees met in June of 1983 to consider all comments and have prepared amendments to the

Standards

for digital

topographic

data

215

draft standards. The technical committees recommended that a minimum of two pilot projects be carried out to convert a set of digital topographic data produced by separate agencies to the proposed national standards. It was felt that such a pilot project would reveal operational problems which come out only in practical applications. Based on results of the pilot projects, improvements to the standards will be incorporated before publication. It is intended to maintain and up-date standards by means of a permanent secretariat that will receive and process comments and requests for incorporation of new features and assign new codes. It is our intention to have a dynamic standard which will be continuously amended and improved to reflect the changing needs of the digital mapping community.