National Mapping Program

USGS Digital Cartographic 

Data Standards

Overview and USGS 

Activities

Geological Survey 

Circular 895-A
USGS DIGITAL CARTOGRAPHIC DATA STANDARDS

TJSGS Circular 895-A: Overview and USGS Activities

B: Digital Elevation Models

C: Digital Line Graphs from l:24,000-Scale Maps

D: Digital Line Graphs from l:2,000,000-Scale Maps

E: Land Use and Land Cover Digital Data

F: Geographic Names Information System

G: Digital Line Graph Attribute Coding Standards

Questions regarding availability and ordering of US GeoData (all

types of digital cartographic and geographic data produced and

distributed by the U.S. Geological Survey) should be addressed to:

User Services Section

National Cartographic Information Center

U.S. Geological Survey

507 National Center

Reston, Virginia 22092

Technical questions and comments should be addressed to:

Chief, National Mapping Division 

U.S. Geological Survey 

516 National Center 

Reston, Virginia 22092

Any use of trade names and trademarks in this publication is for 

identification purposes only and does not constitute endorsement by the 

U.S. Geological Survey.
OVERVIEW AND USGS ACTIVITIES 

By Robert B. McEwen, Hugh W. Calkins, and Benjamin S* Ramey

USGS Digital Cartographic Data Standards 

Edited by Robert B. HcEwen, Richard E. Witmer, and Benjamin S* Ramey

Geological Survey Circular 895-A

1983
United States Department of the Interior

WILLIAM P. CLARK, Secretory

Geological Survey

Dallas L. Peck, Director

First printing 1983 

Second printing 1983 

Third printing 1984

Library of Congress Cataloging in Publication Data

McEwen, Robert B.

US6S digital cartographic data standards.

(Geological Survey circular; 895-A)

Bibliography: p.

Supt. of Docs, no.: 119.4/2:895-A

1. Cartography Data processing. I. Ramey, Benjamin S. II. Calkins, Hugh W. III. Title. IV. Series.

QE75.C5 no. 895-A 557.3s [526'.028'54] 83-600139

[GA102.4.E4]

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
FOREWORD

In recent years, the disciplines of cartography and geography have undergone a rapid and striking reorientation as the 

techniques for digital collection and manipulation of data have 

evolved from fledgling laboratory procedures into dominant and 

driving forces that now pervade the disciplines. Digital techniques have provided a variety of new and powerful capabilities 

to digitally collect, manipulate, analyze, and display spatial 

data. However, this evolution also has introduced a number of 

new and complex problems. One of the most pressing problems, 

and one which is receiving particular attention at present, is 

the issue of digital cartographic data standards.

The U.S. Geological Survey (USGS) has been actively 

developing digital cartographic and geographic techniques for 

over a decade and has taken significant steps to develop and 

define in-house standards governing the various types of 

digital cartographic data that are being collected and archived 

in a national digital cartographic data base. The in-house 

standards are expressed in the form of specifications documents 

that were prepared to govern collection of the data and in the 

form of user guides that were prepared for distribution with 

the data.

In an effort to fulfill lead agency requirements for 

promulgation of Federal standards in the earth sciences, the 

documents have been assembled with explanatory text into this 

USGS Circular consisting of separately bound chapters. This 

Circular describes some of the pertinent issues relating to 

digital cartographic data standards, documents the digital 

cartographic data standards currently in use within the USGS 

National Mapping Division, and details USGS efforts to define 

national digital cartographic data standards.

Chapter A is an overview in which the major issues involved 

in developing digital cartographic data standards are discussed 

and the activities of the USGS related to digital cartographic 

data production and standards development are described in 

detail. Succeeding chapters comprise the pertinent documents 

that establish USGS in-house standards for the various types of 

digital cartographic data currently produced by the National 

Mapping Division that is, digital elevation data, digital 

planimetric data, digital land use and land cover data, and 

digital geographic names data.

This compendium of relevant material is prepared to serve 

as a benchmark and to assist ongoing efforts to establish 

acceptable standards and conventions for both Federal agencies 

and the public.

Dallas L. Peck

Director,

U.S. Geological Survey 

Department of the Interior

R. B. Southard

Chief,

National Mapping Division 

U.S. Geological Survey

111
PREFACE

This Circular is the result of the efforts of numerous individuals who have contributed to the research, development, and 

preparation of various digital cartographic and geographic standards for the National Mapping Division of the U.S. Geological 

Survey. The individuals named as chapter authors represent both 

the originators of the various concepts as well as the writers 

who expanded and clarified these ideas. Their contributions, 

either to the concepts or the writing, are of such magnitude as 

to warrant crediting as authors.

Atef A* Elassal was largely responsible for the original 

data structures and computer file formats that are used for the 

Digital Line Graphs and Digital Elevation Models. The attribute 

coding scheme was first developed by members of the Digital 

Applications Team under the direction of Robert B. McEwen. The 

Geographic Names Information System was conceived and developed 

by Sam Stulberg and Roger L. Payne. The Geographic Information 

Retrieval and Analysis System was developed by Robin G. Fegeas, 

K. Eric Anderson, Stephen C. Guptill, Cheryl A. Hallam, and 

William B. Mitchell. The small-scale Digital Line Graph data 

structure and attribute coding scheme was developed by Warren E. 

Schmidt and Michael A. Domaratz.

The circular was compiled in part from various user guides 

and technical instructions of the National Mapping Division* 

These documents were originally prepared by several individuals; 

credit is acknowledged to G. Michael Callahan, A. Joan Szeide, 

William R. Allder, Vincent M. Caruso, Hugh W. Calkins, Donna 

Cedar-Southworth, and Cheryl A. Ha11am. The compilation of the 

various guides, instructions, and other material into the 

Circular format was performed with major assistance by Clark H. 

Cramer, Eloise R. Byrd, and Cynthia L. Cunningham.

We acknowledge these substantial contributions that have led 

to this publication.

iv
CONTENTS 

____ Page

Foreword ................................................... ill

Preface .................................................... iv

Abstract ................................................... 1

Overview ................................................... 1

Introduction ........................................... 1

Major issues in developing digital cartographic data

standards ............................................ 2

Background of USGS digital cartographic and geographic

programs ............................................. 4

National Committee for Digital Cartographic Data

Standards ............................................ 5

USGS digital cartographic and geographic standards ..... 6

USGS digital cartographic and geographic data .......... 6

Digital elevation data ............................ 6

Digital planimetric data .......................... 7

Digital land use and land cover data .............. 8

Digital geographic names data ..................... 8

Digital cartography in the USGS National Mapping Division .. 9

Background ............................................. 9

Current concepts and activities ........................ 12

Data structure and data management ..................... 17

Conelusion ................................................. 19

References ................................................. 19

ILLUSTRATIONS

_____ Page

Figure 1. Current mapping process of the USGS National

Mapping Division .............................. 15

2. Proposed future mapping process of the USGS

National Mapping Division ..................... 16
US6S Digital Cartographic Data Standards

OVERVIEW AND USGS ACTIVITIES

By Robert B. McEwen, Hugh W. Calkins, and Benjamin S. Ramey

Abstract

The discipline of cartography is 

undergoing a number of profound changes 

that center on the emerging influence of 

digital manipulation and analysis of 

data. Perhaps the most fundamental 

distinction between the digital representation of cartographic data and the 

conventional printed graphic is the need 

to explicitly and unambiguously code the 

attributes and spatial relationships 

among the various data elements. It is 

also necessary to follow acceptable 

practices for automated data processing. 

These requirements have led to the 

development by the USGS National Happing 

Division of several documents that 

establish in-house digital cartographic 

standards.

In an effort to fulfill lead agency 

requirements for promulgation of Federal 

standards in the earth sciences, the 

documents have been assembled with 

explanatory text into a USGS Circular. 

This Circular describes some of the 

pertinent issues relative to digital 

cartographic data standards, documents 

the digital cartographic data standards 

currently in use within the USGS, and 

details the efforts of the USGS related 

to the definition of national digital 

cartographic data standards. It consists 

of several chapters; the first is a 

general overview, and each succeeding 

chapter is made up from documents that 

establish in-house standards for one of 

the various types of digital cartographic 

data currently produced.

OVERVIEW 

INTRODUCTION

In recent years the disciplines of 

cartography and geography have undergone a rapid and striking reorientation 

as the techniques for digital collection and manipulation of cartographic 

and geographic data have emerged from 

fledgling laboratory procedures into 

dominant and driving forces that now 

pervade the disciplines. This reorientation has accelerated since the 

late 1970's with rapid advances in minicomputer and microcomputer technology and 

a steady downward trend in hardware 

prices that have placed digital spatial 

analysis capabilities within the reach 

of ever-increasing numbers of earth 

scientists and land managers. Digital 

techniques have provided the disciplines 

with a variety of new and powerful capabilities to digitally collect, manipulate, analyze, and display spatial data. 

However, this emergence has also introduced a number of new and complex 

problems. One of the most pressing 

problems, and one which is receiving 

particular attention at present, is the 

issue of digital cartographic data 

standards.

The U.S. Geological Survey (USGS) has 

been actively developing digital cartographic and geographic techniques for 

over a decade and has taken significant 

steps to develop and define in-house 

standards governing the various types of 

digital cartographic data that are being
collected and archived. The USGS is also 

actively supporting ongoing efforts to 

define digital cartographic data 

standards applicable throughout the 

industry.

The purpose of this Circular is to 

describe some of the pertinent issues 

relative to digital cartographic data 

standards, to document the digital cartographic data standards currently in use 

within the USGS, and to detail the 

efforts of the USGS related to the definition of national digital cartographic 

data standards. It consists of several 

chapters. This first chapter is composed 

of two parts. The first part discusses 

the issues involved in developing digital 

cartographic standards, and summarizes 

the present USGS activities related to 

the development of such standards as a 

part of current digital data production 

programs. The second part presents a 

historical summary of digital cartographic activities at the USGS. Succeeding chapters are articles, user 

guides/ and coding documents that have 

been separately prepared but which should 

be assembled in a single set of references. This compendium of relevant 

material is prepared to serve as a useful 

benchmark and to assist ongoing efforts 

to establish acceptable standards and 

conventions both for Federal agencies 

and the public. The documents that make 

up the succeeding chapters of this 

Circular represent the status of USGS 

digital cartographic data standards at 

this time and were developed to govern 

operational production programs for 

digital cartographic data collection.

As computer technology evolves, and 

as the disciplines of cartography and 

geography gain experience in the application and adaptation of digital techniques, the needs of those who use 

digital cartographic data will change. 

USGS digital cartographic data standards 

will evolve to meet the changing needs.

MAJOR ISSUES IN DEVELOPING 

DIGITAL CARTOGRAPHIC DATA STANDARDS

In the past, the discipline of cartography has been governed largely by 

conventions established through centuries of practical applications, rather

than by systematically devised standards. 

The standards developed by and for the 

discipline were promulgated primarily to 

assure positional accuracy and consistent 

symbology on the printed map. For example, in the United States, explicit 

written standards have existed since 1941 

pertaining to the positional accuracy of 

maps produced by Federal agencies. In 

that year, the then Bureau of the Budget 

issued the "Standards of Accuracy for a 

National Map Production Program." This 

document was subsequently revised and 

retitled on June 17, 1947, as the "United 

States National Map Accuracy Standards" 

and remains in effect today. Similarly, 

the symbology on printed topographic maps 

produced by the Geological Survey has 

been controlled largely through issuance 

of in-house documents that specify in 

considerable detail the criteria for 

graphic representation of the various 

features and other information shown on 

a map. Conscientious adherence to these 

very basic standards for accuracy and 

symbology in the production of the USGS 

Topographic Map Series has resulted in an 

accurate and dependable set of multipurpose base maps of remarkably uniform 

quality and appearance.

Today, however, the cartographer must 

deal not only with the traditional 

printed map, but also with a vast and 

rapidly growing volume of cartographic 

data in digital form. The basic standards of positional accuracy and consistent graphic representation that have so 

ably governed the production of printed 

maps in past years are certainly vital in 

defining and understanding the emerging 

world of digital cartographic data. 

However, as experience with digital cartographic data has grown, it has become 

clear that the positional and symbolization standards devised for the printed 

map provide a less than adequate guide 

when translated literally for the digital 

environment.

Perhaps the most fundamental distinction between the digital representation 

of cartographic data and the conventional 

printed map is the need, in the digital 

realm, to explicitly and unambiguously 

encode the spatial relationships among 

the various elements of the data. In 

graphic form, these relationships are 

implicitly conveyed and usually grasped
by even the novice map user. In the 

digital realm, the explicit coding of 

spatial relationships is referred to as 

topological structuring and is absolutely 

necessary if the digital cartographic 

data are to be employed for the spatial 

analysis of geographic relationships. 

Topology, as defined for digital cartography and spatial analysis, requires that 

all lines be explicitly linked to nodes 

(ends of lines or line junctions) and 

that all areas be explicitly linked to 

their bounding lines (arcs). Although 

the concept is relatively simple to state 

and to understand, there are several 

distinct and viable methods and structures for digitally encoding these 

spatial relationships. Clearly, a standard for topological coding would be 

desirable if a proliferation of incompatible representation schemes is to be 

avoided. However, for both historical 

and technical reasons there are currently 

two major structuring schemes in use in 

the US6S.

One major scheme is oriented toward 

efficient digital representation of 

polygon (areal) cartographic data 

characterized by lines delimiting 

nonoverlapping homogeneous characteristics. The lines have no meaning other 

than to delimit the polygons. This 

scheme was developed for digital 

encoding via the Geographic Information 

Retrieval and Analysis system (GIRAS). 

The structure is described in detail in 

Chapter E of this Circular. The other 

major scheme is oriented toward efficient 

digital representation of planimetric 

cartographic data that consist of point 

(zero-dimensional), linear (one-dimensional), and areal (two-dimensional) 

features. In this scheme, lines may 

delimit homogeneous areas as in the 

polygon-oriented scheme, but more often 

the lines define inherently linear 

features such as roads and streams. 

This scheme was developed for digital 

encoding via the unified Cartographic 

Line Graph Encoding System (UCLGES) of 

the planimetric information found on the 

various USGS Topographic Hap Series. The 

structure is described in detail in Chapters C and D of this Circular. Considerations for either resolving the differences in favor of either a single 

structure or for the acceptance of a 

limited number of schema with suitable

translation software are currently under 

discussion.

A second distinction between the traditional map and the digital representation of the map is the need, in digital 

representation, to numerically encode the 

attributes of the cartographic data that 

are normally conveyed to the reader of a 

printed map via color, line weight, 

varying symbology, labels, and so on. 

Some types of cartographic attributes 

are relatively easy to encode digitally. 

Highway classifications, route numbers, 

and the population of a town are examples. Other types are much more difficult. The notion of continuity of a 

stream or highway network is easily conveyed graphically through the varied symbolism on a printed map but is extremely 

difficult and unwieldy to define numerically in the digital representation. 

The concept of feature coincidence, such 

as a boundary along a highway or stream, 

is an aspect of cartographic information 

that is readily portrayed on the printed 

map but is sometimes quite difficult to 

unambiguously encode in the digital 

cartographic representation. As is the 

case with topology, a virtually limitless 

number of schemes are technically feasible for digitally encoding cartographic 

attributes. The actual numbers used to 

represent a feature are of far less 

concern than the global rationale of the 

coding strategy. Without a governing 

standard, a variety of mutually incompatible schemes will doubtlessly arise and 

will have a profound influence on future 

use of the data in geographic information 

systems.

A third crucial distinction between 

the traditional printed map and cartographic data in digital form arises from 

the fact that digital cartographic data 

must consist of a serial coded bit stream 

of information; that is, the data are in 

fact irrevocably, and sometimes inhospitably, bound into the existing computer 

environment that was not developed with 

spatial data handling in mind. Only as 

such, can digital cartographic data be 

manipulated via computer hardware and 

associated operating system software 

developed and produced by the automated 

data processing (ADP) industry. If the 

discipline of cartography is to effectively exploit technological advances in 

the ADP field, digital cartographic data
must be structured, coded, and formatted 

to be reasonably compatible with data 

standards set forth by the ADP industry.

Within the three broad issues of 

topological structuring, attribute 

coding, and compatibility with ADP 

standards, several specific concerns 

related to standardization have 

surfaced. These are:

1. Terminology A precise definition 

of technical terms is necessary to 

insure effective communication.

2. Data Interchange Format The high 

cost of collecting digital cartographic data requires data exchange 

to minimize duplication of effort 

and maximize the use of generalpurpose data bases. This in turn 

has precipitated a need for common 

interchange formats.

3. Data Quality Digital cartographic 

data quality depends on a number of 

factors, including the quality, 

accuracy, scale, and currency of the 

source materials, the data collection 

quality controls, and procedures 

used to check and verify the data. 

Ideally, every distinct unit of 

digital cartographic data should include explicit information defining 

the quality of the data set. Standards are needed to define levels of 

quality with a uniform interpretation.

4. Compatability With Standards in 

Related Disciplines Digital cartographic data standards should be compatible with similar standards set 

forth by the various related disciplines, including, for example, 

remote sensing, photogrammetry, 

geodetic and land surveying, digital 

image processing, and computer 

graphics.

BACKGROUND OF USGS DIGITAL 

CARTOGRAPHIC AND GEOGRAPHIC PROGRAMS

The USGS has Federal responsibility 

for preparing and making available multipurpose maps and fundamental cartographic 

data to meet the requirements of users 

throughout the United States. The role 

of the USGS National Happing Division 

(NMD) in this mission is to prepare and

make available topographic maps and associated base category data, such as hydrography, hypsography, and transportation systems. The NMD is actively 

adopting computer technologies to 

support this mission (Southard and 

Anderson, 1983; Starr and Anderson, 

1982).

Geological Survey activities in 

digital cartography and geography began 

in the early 1970's with research work 

in the then fledgling field of automated 

spatial data analysis. Production of 

digital land use and land cover data 

began in 1973 in response to increasing 

demands by natural resource managers for 

development of digital techniques to 

collect, manipulate, and analyze earth 

science data. This program has evolved 

considerably over the years but continues today.

As the body of knowledge in digital 

spatial data analysis grew, it became 

apparent that fundamental cartographic 

data were needed in digital form to 

serve as a reliable reference base for 

digital spatial analysis. In addition, 

it was anticipated that increasing use of 

automated equipment and digital cartographic data would improve the timeliness 

and flexibility of map preparation with a 

possibility of eventually reducing overall costs. Accordingly, the concept of a 

National Digital Cartographic Data Base 

(NDCDB) was adopted, and a project was 

begun in 1977 to develop the capability 

to digitize, manage, and distribute base 

cartographic data consistent with the 

content and detail of the standard USGS 

l:24,000-scale Topographic Map Series 

(McEwen, 1980). In 1978 the USGS began 

collecting these base category digital 

cartographic data in an operational 

program. The now familiar digital line 

graphs (DLG's) and Digital Elevation 

Models (DEM's) corresponding to content 

and accuracy of standard 7.5-minute quadrangles were the primary products of the 

program.

Other programs begun by the late 

1970 "s include development of a Geographic Names Information System (GNIS) 

and development of a national small-scale 

digital cartographic data base. Work on 

the GNIS was begun with the objective of 

building a digital data base of all the 

names used on the l:24,000-scale
Topographic Map Series. Collection of 

data for the national small-scale digital 

cartographic data base was begun in 1979 

from the 1:2,000,000-80316 sectional base 

maps of The National Atlas of the United 

States of America, and the first phase of 

this project was completed in mid-1982.

From the outset, it was recognized 

that basic standards governing data 

coding, structure, and accuracy were 

needed to insure the integrity and consistency of data sets. Accordingly, as 

each distinct digital cartographic data 

type was conceived and data production 

initiated, strict standards were developed in the form of in-house specifications pertaining to the accuracy, data 

structure, and feature coding to be used. 

It was also decided that USGS in-house 

standards should emphasize anticipated 

long-term future data requirements, accuracies, data content, and technical 

environment to build a comprehensive archival data base from which applicationsoriented data could be derived. The 

specifications and other written documents then formed the basis for several 

descriptive user guides that were prepared for distribution with the data.

These specifications and their related user guides govern the current 

collection, processing, and distribution 

of the various types of digital cartographic data that have been and are being 

archived in the NDCDB. In the definition 

of each data type, a concerted effort was 

made to anticipate trends and hence maximize the useful life of the standards; 

mechanisms for expansion and evolution 

were included wherever feasible in recognition of the inevitability of change.

As the application of computer technology to the disciplines of cartography 

and geography has burgeoned in recent 

years, so has application of automated 

methodologies in kindred disciplines 

within the earth sciences (Frederick and 

Anderson, 1983). Recognition by Federal 

agencies of the pressing need for standardization of data elements and representations used in all automated earthscience systems resulted in the issuance 

of a Memorandum of Understanding (MOU) 

signed in February 1980 by the National 

Bureau of Standards of the Department of 

Commerce/ and by the USGS of the Department of the Interior.

Under the terms of this MOU, the USGS 

assumed leadership in developing, defining, and maintaining earth-science data 

elements and their representation standards for use in the Federal establishment, in addition to developing and 

maintaining standards, the USGS reviews 

and processes all requests referred by 

the National Bureau of Standards for exceptions, deferments, and revision of 

standards applicable to Federal earthscience information systems; assists the 

National Bureau of Standards in assessing 

the need, impact, benefits, and problems 

related to the implementation of standards being considered for development, 

or already developed, for use in the 

earth sciences; and works with other 

agencies in developing new data standards 

in the earth sciences.

Given the leadership role assigned to 

the USGS under the terms of this MOU and 

the specific tasks that are part of the 

National Mapping Program, the NMD has 

assumed responsibility for developing and 

maintaining cartographic and geographic 

data elements and their representation 

standards for use in the Federal 

e stabli shment.

NATIONAL COMMITTEE FOR DIGITAL 

CARTOGRAPHIC DATA STANDARDS

Ultimately, the effectiveness of any 

standard is a function of the degree of 

acceptance accorded by the user community. This degree of acceptance, in 

turn, depends upon the responsiveness of 

the standard to demonstrated needs. Individual users will bear some temporary 

inconvenience and cost of adhering to a 

newly instituted standard if it is perceived that the benefit to the community 

as a whole promises an eventual return 

exceeding the initial investment of time 

and effort. Recognizing the need to involve the user community in the digital 

cartographic standards process, the USGS 

is actively supporting the work of the 

National Committee for Digital Cartographic Data Standards <NCDCDS) 

(Moellering, 1983).

Established in January 1982 and operating under the auspices of the American 

Congress on Surveying and Mapping, the 

NCDCDS consists of a steering committee
and working groups on (1) Data Organization, (2) Data Set Quality, (3) Features, 

and (4) Terms and Definitions. Additional working groups may be created as 

needs are identified. The membership 

consists of professionals from Federal, 

State, and local agencies; private enterprise; and the academic community. The 

stated goal of the NCDCDS is to provide 

a professional forum for all involved 

public agencies and professional individuals to express their opinions, assessments, and proposals concerning digital 

cartographic data standards. The Committee will be requested to review these 

US6S standards; after sufficient time 

for circulation, discussion, reformulation, and comment, they will be submitted 

to the National Bureau of Standards for 

consideration as Federal Information 

Processing Standards (FIPS).

The primary tasks of each working 

group are:

1. To assess the state of current 

knowledge and understanding in the 

technical area;

2. To define any gaps in such knowledge 

and understanding necessary to 

specify digital cartographic 

standards in that area;

3. To invite presentations and opinions 

from all interested parties relating 

to its standards area;

4. To prepare technical working papers 

of their deliberations and discussions; and

5. To propose digital cartographic data 

standards for its technical area.

On completion of these tasks by the 

individual working groups, the steering 

committee will issue reports setting 

forth the proposed standards. It is anticipated that the work of the NCDCDS, 

with input from the entire user community, will result in digital cartographic 

data standards acceptable and beneficial 

to the entire cartographic community.

USGS DIGITAL CARTOGRAPHIC AND 

GEOGRAPHIC STANDARDS

In accordance with stated objectives, 

the USGS National Mapping Division is 

producing four basic types of digital 

cartographic and geographic data to meet

the requirements of users throughout the 

United States:

1. Digital elevation data;

2. Digital planimetric data;

3. Digital land use and land cover 

data; and

4. Digital geographic names data.

Strict standards pertaining to accuracy, data structure, and feature codes 

have been developed in the form of both 

in-house specifications and data user 

guides to govern the collection and 

dissemination of each data type. A copy 

of each specification and user guide 

applicable to the four data types listed 

above is included as a chapter in this 

Circular. The USGS has taken this initial step in the standardization process 

to insure data integrity and consistency, 

to aid in the interpretation of data 

files, and to thereby encourage acceptance and use of a standardized data 

base, the NDCDB.

At present, all user guides and specifications describing the standards for 

the various NMD digital cartographic data 

types are in draft form pending review. 

On completion of this internal review, 

the documents will be reviewed by the 

USGS Data Standards Committee, other 

USGS Divisions, the Department of the 

Interior, and the NCDCDS. The USGS also 

intends to solicit comments and advice 

from other Federal and State agencies, 

private industry, the academic community, 

and the professional societies in the 

mapping field. Ultimately, the documents 

will be submitted to the National Bureau 

of Standards for adoption as standards 

applicable throughout the Federal 

establishment.

USGS DIGITAL CARTOGRAPHIC 

AND GEOGRAPHIC DATA

Succeeding chapters of this Circular 

contain considerable detailed information 

about each of the four data types. However, a brief synopsis follows.

Digital Elevation Data

Digital elevation data are produced and distributed in the form of 

digital elevation models (OEM's) each
corresponding in coverage to the standard 

USGS 7.5-minute topographic quadrangles, 

and digital terrain tapes (DTT's) and 

arc-second OEM's corresponding to 

1:250,000-scale topographic maps.

A 7.5-minute DEM may be created from 

a number of data sources, such as map 

contour overlays, profiles or terrain 

models scanned manually in photogrammetric equipment, or from automated 

orthophoto or stereoplotting equipment 

(Allder and others, 1983). Currently, 

the majority of the 7.5-minute OEM's are 

created using digitizing orthophoto 

equipment and consist of elevation values 

spaced at regular 30-m intervals, and 

referenced in the Universal Transverse 

Mercator (UTM) coordinate system. The 

standard DEM format, however, does provide for randomly spaced elevation values 

and a variety of coordinate referencing 

systems.

The 7.5-minute OEM's are archived in 

the NDCDB according to two distinct 

levels of vertical accuracy: (1) less 

than 7-m vertical root-mean-square error 

(RMSE) and (2) 7- to 15-m vertical RMSE. 

The 7-m vertical RMSE was determined to 

be a reasonable and attainable standard 

under a variety of terrain conditions and 

instrument constraints from 1:80,000- 

scale high-altitude aerial photographs.

The USGS distributes digital elevation data produced by the Defense Mapping 

Agency (DMAf from 1:250,000-scale topographic maps in the form of digital terrain tapes (DTT's) and arc-second OEM's.

Digital terrain tapes were produced 

by the DMA by digitizing the contours, 

ridgelines, and drains from 1:250,000- 

scale topographic maps and subsequently 

interpolating elevations to the nearest 

foot at 0.01-inch intervals at map scale. 

The 0.01-inch spacing corresponds to a 

ground distance of 63.5 m between elevation values. The data are referenced 

horizontally in the UTM coordinate 

system. Each DTT represents a 1° x 1° 

block that corresponds to the east or 

west half of the source 1:250,000-scale 

map. The DTT's are distributed by the 

USGS, as produced by the DMA, and do not 

conform to the standard USGS DEM format.

Arc-second OEM's are produced by the 

DMA by updating and reformatting existing 

DTT's, where feasible, and by scanning 

contours, ridgelines, and drains from

1:250,000-scale maps and subsequently 

interpolating where DTT coverage is nonexistent or inadequate. Elevation values 

are recorded to the nearest meter and are 

spaced at intervals of 3 seconds of arc, 

referenced horizontally in latitude and 

longitude coordinates. Three seconds 

of arc represents approximately 90 m in 

the north-south axis and a variable 

dimension (approximately 90 m at the 

Equator to 60 m at 50° latitude) in the 

east-west axis due to convergence of the 

meridians. Like DTT's, arc-second OEM's 

represent 1° x 1° blocks corresponding 

to the east or west half of the source 

1:250,000-scale map, except in the State 

of Alaska, where the block size varies 

with latitude. Arc-second OEM's are 

structured to conform to the standard 

USGS DEM format.

Although interpolated elevation 

values are recorded to the nearest foot 

in DTT's and to the nearest meter in arcsecond OEM's, the vertical accuracy of 

values in both the DTT's and arc-second 

OEM's is limited to the inherent accuracy 

of the contours on the 1:250,000-scale 

map used as the source for derivation.

Digital Planimetric Data

Digital planimetric data are produced 

and distributed in the form of digital 

line graphs (DLG's). Two distinct types 

of DLG data are currently produced: (1) 

large-scale DLG data digitized from 

1:24,000-scale USGS topographic quadrangles and (2) small-scale DLG data 

digitized from the 1:2,000,000-scale sectional maps of The National Atlas of the 

United States of America. The basic 

applications of DLG data are to support 

automation of the cartographic processes 

and automated spatial data analysis.

The DLG file structure is designed to 

accommodate virtually all categories of 

planimetric data represented on a conventional line map. Point, line, and area 

data types are accepted. Each distinct 

data category (such as boundaries, hydrography, and transportation) is stored 

as a separate file or subfile in the 

NDCDB. These separate files are somewhat 

equivalent to the printing separates 

used in the conventional map production 

process. The data are classified at one
of three levels according to the editing, 

enhancements, and spatial structuring 

performed on the files. The attribute 

coding scheme is open-ended and can be 

expanded as needed.

The DLG data format and structure 

were designed to contain, in digital 

form, the planimetric data shown on the 

standard USGS 7.5-minute topographic 

quadrangles. The attribute coding 

scheme is designed to accommodate basic 

cartographic data categories such as 

elevation, transportation, or boundaries, as well as additional thematic 

data categories.

The small-scale DLG data were digitized from the l:2,000,000-scale National 

Atlas sectional base maps to meet the expressed needs of the USGS and other user 

agencies for a complete small-scale 

national data base. These DLG data files 

are available in a topologically structured format suitable for use with geographic information and spatial data 

analysis systems. The data are also 

available in a simplified graphics format 

(information defining topological structure is omitted) designed especially for 

automated graphics production. Both 

formats include feature codes assigned to 

facilitate automated production of base 

maps and special-purpose graphics at 

scales ranging from 1:2,000,000 to 

1:10,000,000. Two capabilities are built 

into this feature coding scheme: (1) the 

size of a feature is coded to permit 

selection of features appropriate for the 

output scale and (2) the type of feature 

is coded to permit logical aggregations 

by types (Selden and Domaratz, 1983). 

Coverage is nationwide, and the data are 

stored in multistate regional blocks to 

limit discrete files to a manageable size 

while minimizing edge-join problems in 

applications requiring data aggregation. 

The total number of blocks is 21; 15 for 

the conterminous united States, 5 for 

Alaska, and 1 for Hawaii.

land use and land cover in polygon 

format, and the digital data are accordingly structured in a highly compressed 

arc-segment polygon format designed to 

facilitate digital manipulation and 

analysis using the computer programs of 

the Geographic Information Retrieval and 

Analysis System (GIRAS) (Mitchell and 

others, 1977). In tandem, the digital 

land use and land cover data and the 

GIRAS software constitute a functional 

geographic information system suitable 

for automated analysis of a variety of 

resource and planning problems.

A separate digital data file is 

created for land use and land cover and 

each of four associated data categories: 

(1) political units; (2) census county 

subdivisions; (3) hydrologic units; and 

(4) Federal land ownership. Each file 

consists of arcs and nodes defining the 

perimeters of nonoverlapping areas, and 

numeric codes (polygon labels) that 

identify the category to which each area 

(polygon) belongs. To minimize data 

volume, arcs separating polygons are 

digitized only once. A system of pointers is used to define the topological 

structure and uniquely identify the arcs 

that must be connected to form a given 

polygon.

The GIRAS software provides the capability to perform a variety of manipulation and analysis functions with the 

digital land use and land cover data including rotation, translation, and 

scaling of coordinates; conversion to 

geographic coordinates and from geographic coordinates to specified map projections; conversion from the arc-segment 

polygon structure to grid cells; conversion to standard polygon format; production of area summary statistics from 

polygon or grid-cell data; production of 

border (perimeter) and adjacency statistics; lengths of particular polygon types 

from polygon data; and production of a 

variety of output graphics.

Digital Land use and Land Cover Data

Digital land use and land cover data 

are derived from land use and land cover 

and associated maps (1:250,000- and 

1:100,000-scale). The source maps depict

Digital Geographic Names Data

Digital geographic names data are 

collected and archived via a multipurpose software and data base complex 

collectively termed the Geographic Names
Information System (GNIS) (Orth, 1980). 

The GNIS was conceived and developed to 

meet six basic objectives:

1. To assist the U.S. Board on 

Geographic Names in establishing 

uniform name usage throughout the 

Federal sector;

2. To provide a computerized index of 

names found on maps compiled by 

Federal, State, and private 

organizations ;

3. To eliminate the need to create 

special-purpose data bases containing similar information;

4. To provide an interface for 

integration of data from other 

systems for multidisciplinary use;

5. To provide a standard for digital 

representation of geographic names 

data; and

6. To meet Federal public information 

requirements prescribed by law.

The master plan for the 

includes five distinct data bases:

GNIS

1. National Geographic Names Data Base;

2. USGS Topographic Map Names Data Base;

3. Generic Data Base;

4. National Atlas Data Base; and

5. Board on Geographic Names Data Base.

The first four data bases are currently active and addressed in Chapter F. 

The fifth data base and appropriate documentation will be added at a later date.

The National Geographic Names Data 

Base is the primary data component of the 

GNIS and consists of descriptive information pertaining to all named features 

(except roads, communication towers, and 

triangulation stations) found on the maps 

of the USGS Topographic Map Series. Additional information garnered from other 

graphic and textual sources is being 

added on a daily basis. The National 

Geographic Names Data Base is divided 

into 57 files representing the 50 States, 

six territories, and the District of 

Columbia. AS many as 29 distinct data 

elements may be recorded to describe 

each named feature.

The USGS Topographic Map Names Data 

Base, as the name suggests, contains descriptive information pertaining to the 

official names of the individual map

sheets in the USGS Topographic Map 

Series. The data elements include descriptors for current and historical 

names, location and extent, and scale.

The Generic Data Base is structured 

to serve as a research tool and as a depository for textual descriptive information for the GNIS. A total of 61 

feature categories (designators) are 

defined and cross-referenced to specific 

types of features found on published 

maps. This data base also contains text 

describing unusual generic information 

(location, application, reason for 

unusual application) and a complete bibliography of source materials (other than 

the USGS Topographic Map Series) employed 

in the compilation of the GNIS.

The National Atlas Data Base currently contains descriptive information 

pertaining to the geographic names found 

in the index of The National Atlas of 

the United States of America. This data 

base is intended and structured to eventually serve as an abridged version of 

the National Geographic Names Data Base.

Access to the various data bases 

within the GNIS is accomplished via the 

General Information Processing System 

(GIPSY) software developed at the University of Oklahoma. GIPSY provides 

searching and sorting capabilities that 

allow the user to selectively extract 

information and assemble logical aggregations of data.

DIGITAL CARTOGRAPHY 

IN THE NATIONAL MAPPING DIVISION

BACKGROUND

The National Mapping Division of the 

USGS is actively adopting computer technologies to support its mission of collecting cartographic data at a national 

level for the United States and its territories. Early, it was recognized that 

traditional cartographic methods would 

someday be replaced by predominantly 

digital techniques, and the concept of a 

national digital cartographic data base 

was embraced during the mid-1970's. The 

desirability of such a data base was generally accepted, but the process of turning such a general concept into reality 

was recognized to be fraught with both
technical and procedural difficulties. 

This review is a progress report on the 

NMD experience to date outlining what 

has been accomplished, the issues 

addressed, the concepts and strategies 

adopted, and finally some of the unresolved problems that are still facing us.

The USGS through the National Mapping 

Program has the objective of preparing 

and making available multipurpose maps 

and fundamental cartographic data to meet 

the requirements of users throughout the 

United States. The NMD has concentrated 

its efforts on base category data as 

found on topographic maps, such as hypsography, hydrography, and transportation 

systems. Other Federal agencies and 

other USGS divisions are responsible for 

collecting additional map data of public 

value, identified as nonbase categories. 

The National Ocean Service is charged 

with the responsibility for geodetic 

surveys and for the preparation of aeronautical and nautical charts. The 

Defense Mapping Agency is responsible for 

maps and charts on a worldwide basis to 

meet national defense requirements. The 

Water Resources Division and the Geologic 

Division of USGS collect data and prepare 

thematic maps of hydrologic and geologic 

information. The Bureau of Land Management has responsibility for cadastral 

surveys related to the U.S. Public Land 

Survey System.

The principal activities associated 

with the NMD portion of the National 

Mapping Program can be conveniently identified by the conventional types of map 

products produced--!:24,000-scale topographic maps (the largest activity and 

the largest scale national map product), 

1:24,000-scale orthophotoquads, and 

1:100,000- and 1:250,000-scale regional 

maps. There is also significant activity 

in land use and land cover mapping at 

1:250,000-scale, State and national 

small-scale maps, and a variety of 

special maps, including image maps prepared from Landsat data. A major new 

activity is the development and production of digital (computer-compatible) 

base category cartographic data to support automated cartography and automated 

spatial data analysis.

It may be useful to list the base 

data categories found on the 1:24,000- 

scale maps as these categories are found

in the official manual that authorizes 

the National Mapping Program.

1. Reference systems Geographic and 

other coordinate systems not including the public land survey 

system network.

2. Hypsography Contours, slopes, 

elevations.

3. Hydrography -- Streams and rivers, 

lakes and ponds, wetlands, reservoirs, shorelines.

4. Surface cover Woodland, orchards, 

vineyards (general categories only).

5. Nonvegetative features Lava rock, 

playas, sand dunes, slide rock, 

barren waste areas.

6. Boundaries Political jurisdictions, national parks and forests, 

military reservations. This category 

does not fully set forth land ownership or land use.

7. Transportation systems Roads, 

railroads, trails, canals, pipelines, 

transmission lines, bridges, tunnels.

8. Other significant manmade structures Buildings, airports, dams.

9. Identification and portrayal of geodetic control, survey monuments, 

other survey markers, landmark structures and objects.

10. Geographic names.

11. Orthophotographic imagery.

Not included in this list is the land 

use and land cover data that were authorized separately to the USGS and should 

now be considered a NMD responsibility.

The USGS has had several separate 

research and development activities in 

digital cartography and automated spatial 

data analysis (Guptill, 1978). Since the 

early 1970's, the USGS has done significant work in developing the theory and 

practice for automated spatial data analysis. Experiments using Landsat data for 

land use and land cover evaluation were 

started and continue today. In addition, 

a practical system of computer programs 

was developed to batch process the land 

use and land cover data digitized with 

automated line-following equipment and to 

produce topologically structured polygon 

data files. This was a significant development for it allowed the land use and 

land cover polygon data then being compiled in graphic form to be entered into

10
the computer for sophisticated geographic 

spatial analysis. Techniques also were 

developed to convert the files of polygons into a regular cellular format. 

Thus it became possible to efficiently 

overlay multiple data sets.

A Digital Applications Team was 

formed in 1977 to focus in a single 

group the scattered ongoing activities 

and to perform further research, development, and applications (McEwen, 1980). 

The goal was to develop a prototype capability to digitize, manage, and distribute cartographic data represented by the 

content and detail of the standard USGS 

l:24,000-scale topographic map. This required that numerous systems of computer 

programs be developed to process cellular 

arrays (such as elevation data), networks 

(such as streams), areas (such as political units), and points (such as cultural 

features). It was determined that the 

resulting files should be topologically 

structured and that an extensive set of 

attribute codes would be required for the 

extremely high level of information contained on a map. Some types of map 

information are relatively easy to 

encode a highway classification, for 

example while other types are more 

difficult. Maintaining the notion of 

continuity of a stream network or a highway grid (so easy to see on a printed 

map) raises many perplexing questions in 

a computer environment. The data categories, such as boundaries, Public Land 

Survey System Net, streams, and transportation from l:24,000-scale maps, were 

digitized manually for a few pilot projects and batch processed into standard 

DLG files for entry into a data base. 

The Division had been operating automated 

orthophoto equipment since the mid-1970's 

for the production of 1:24,000-scale 

orthophotoquads from high-altitude aerial 

photographs, and a byproduct of this 

operation is an array of digital elevations that are processed into OEM's. 

Several thousand quadrangles of raw data 

existed on tapes, and procedures were 

developed to process these data and produce a data base.

Recognizing that manual digitizing 

was an expensive roadblock, action was 

initiated to develop an automated raster 

scanning and editing system. The decision to pursue raster technology was made 

with full recognition of the consequent

requirement to develop raster-to-vector 

conversion and editing procedures and 

with the anticipation that a symbiotic 

relationship would develop with digital 

image processing technology.

The Division operates four production 

mapping centers, and each was equipped 

with various pieces of digital equipment 

(manual digitizing equipment, precise 

automatic plotters, multistation interactive editing equipment, minicomputers, 

and teleprocessing terminals). Each 

mapping center initiated production of 

digital data files. After initial 

processing, data are transmitted to the 

mainframe computers in Reston, Va., for 

final processing, topologic structuring, 

and entry into the primary digital cartographic data base in a standardized archival format. The data base system 

consists of a unified set of custom 

cartographic computer programs built 

around the capability of a hierarchical 

data base management system a standard 

capability on the USGS mainframe computer. The custom programs perform 

entry, update, reformatting, retrieval, 

and other housekeeping functions such as 

data security, reports, index maps, and 

internal management of the digital cartographic files.

The introduction of digital equipment into the NMD mapping centers also 

led quite properly to automating various 

phases of the conventional mapping process (Powell, Osick, and Thomas, 1979; 

Troup and Powell, 1979). Stereophotogrammetric plotters equipped with digital 

encoders have been used to produce files 

that, after some editing, can be used to 

photoscribe a base sheet from several of 

the map categories. A voice data terminal allows the stereoplotter operator to 

verbally enter commands and attributes 

without diverting attention from the 

optics or plotter controls. A voice synthesizer is used to provide an auditory 

confirmation of the instructions. While 

the digital stereocompilation process may 

be slightly more expensive than traditional preparation of the usual manuscript copy, the almost total elimination 

of manual scribing results in a cost advantage. At the moment, the digital 

lines and points so produced do not contain all the information needed to build 

a topologically structured cartographic 

data file.

11
The Division has also had under development since the mid-1970's a Geographic Names information System with the 

objective of building a digital data base 

of all the names used on the 1:24,000- 

scale USGS Topographic Map Series (orth, 

1980). The name of a feature is entered 

together with the class of feature {such 

as stream, mountain, or place) and the 

coordinates where the name appears on a 

certain map. Additional data are encoded 

to describe the link to other maps where 

the same feature may be continued (often 

for long distances in the case of features such as rivers). The file also 

contains textual reference to the decision lists maintained by the Board on 

Geographic Names. Data encoding and 

editing are complete for all 50 States. 

The data base will be valuable for automatic type preparation, for production of 

gazetteers, and as a source of data for 

investigating automated names placement 

one of the more expensive map-finishing 

operations that conceptually defies 

automation.

By mid-1979 the various digital research and developmental activities at 

the four mapping centers and within the 

research staff at the Reston headquarters 

of the USGS had developed to the point 

where a major review and assessment were 

needed. The Chief, National Mapping 

Division, therefore appointed a Digital 

Mapping Program Steering Committee to 

develop detailed plans for the Digital 

Mapping Program including the identification and evaluation of research and 

development problems, development of 

alternatives, and the recommendation of 

realistic objectives for the program. 

The intensive review of NMD digital activities by this committee led to the 

recommendations that (1) sufficient 

digital data production capability 

existed to start producing some digital 

data files and (2) a phased program of 

additional research and development would 

be required before the full digital 

mapping program could be implemented.

CURRENT CONCEPTS AND ACTIVITIES

The NMD is now in continuous production with a capability to provide 

digital cartographic and geographic data

at an accuracy and level of detail equivalent to the l:24,000-scale USGS Topographic Map Series for cartographic uses 

(l:250,000-scale for land use and land 

cover data) and tqpologically structured 

to serve geographic information systems. 

Each l:24,000-scale topographic map 

covers a quadrangle of 7.5-minutes of 

latitude and longitude, there are approximately 55,000 maps required to cover the 

conterminous United States and Hawaii, 

in Alaska, except for a few 1:24,000- 

scale maps around Fairbanks, the largest 

scale maps are 1:63,360 (1 inch = 1 

mile). The country is approximately 80 

percent mapped with conventional line 

maps at these scales, and there has been 

a major emphasis over the past decade to 

achieve complete coverage and replace 

some of the smaller scale maps, such as 

some l:62,500-scale maps that date from 

the years immediately following world 

War II. The goal of complete up-to-date 

map coverage is still a number of years 

away; meanwhile, the level of activity in 

map revision is growing. The new capability had to be integrated into these 

ongoing activities*

The scenario that presented itself to 

the NMD had the following objectives:

1. To continue the preparation of conventional line maps by the most 

economic methods;

2. To convert the large amount of 

existing line map data into a 

computer-compatible form;

3. To establish a digital cartographic 

data base that would serve in the 

future as a foundation for geographic information systems; and

4. To reconfigure the conventional 

mapping process to take full advantage of automation, especially as it 

will influence map revision.

A number of secondary objectives also 

have emerged. These include the preparation of a small-scale data base that can 

be used to prepare special graphics and 

index maps of a national scope and the 

development of some data base categories 

for use at intermediate scales, that is, 

1:100,000 to 1:250,000 (Schmidt, 1981; 

Selden and Domatatz, 1983). These primary and secondary objectives introduce 

a number of conflicts that require

12
technological and program-management 

solutions.

The first objective, continuation of 

an economically viable conventional 

mapping program, requires that many of 

the well-established analog photomechanical techniques of map preparation 

be continued, until recently, at least, 

our evaluation of completely digital mapmaking in other mapping organizations 

worldwide indicated that attempts to 

totally automate map preparation usually 

resulted in higher initial costs and that 

the assumed cost advantages in deriving 

other maps at smaller scales or in conducting map revision had yet to materialize. Thus, the (former) Topographic 

Division appeared to be waiting on the 

sidelines while many mapping organizations pursued automated cartography in 

the early 1970*s with the goal of producing a complete digital map. We will 

return to this issue in a moment.

The second objective, to convert the 

large number of existing maps to 

computer-compatible form, presented two 

conceptual problems. The first related 

to the technology to be adopted for 

digitizing. While equipment capable of 

digitizing data at the photogrammetric 

compilation stage of map preparation is 

available, such equipment is not suited 

for digitizing existing map separates 

and is overly restricted by the conventions of the current mapping process. 

Some data categories (for example, boundaries) cannot be obtained from aerial 

photographs, and some doubt exists that 

efficient procedures can be developed to 

allow a plotter operator to capture all 

of the information needed to produce 

topologically structured data files.

The second problem is largely 

economic. until a sufficient number of 

maps are converted to computer-compatible 

form, the proposed applications will not 

be realized. Murphy's Law for cartography has two cardinal postulates: (1) 

map data are always requested by a user 

over unmapped areas and (2) the area of 

user interest always straddles some type 

of zone boundary. Data users' needs 

require the archiving of a large 

"critical mass" of data. Until that 

quantity of data is archived, a great 

deal of the data will go unused, and 

many users may think that it is more

effective for them to independently digitize the data they need. The capital 

Investment to assemble a data base of 

"critical mass" can be quite large and 

the risks, even for a Government organization, are significant. The pressure 

to show short-term effectiveness while 

pursuing an essentially long-term goal 

has all of the elements of private enterprise investment. Thus, the Division has 

adopted a number of digitizing strategies 

for data capture.

These strategies require a rigidly 

defined archival data file structure that 

is used for entering data into the data 

base. This defined structure is necessary to avoid a plethora of data formats 

developed only for an immediate application or for an existing hardware 

configuration.

At the same time, multiple types of 

digitizing equipment were installed and 

software was developed to preprocess the 

data into the standard format. Manual 

digitizing tables continue to be used and 

can be quite effective for data categories consisting of many straight lines 

or single points. Some manual digitizing 

tables are integral components of interactive editing systems. A number of 

photogrammetric plotters have been retrofitted with digitizers to obtain the 

usual data categories (such as transportation systems, drainage, and contours) 

that are depicted during compilation of 

new maps. Digitizing also was conducted 

under contract where automated linefollowing equipment could be used effectively. The equipment used to prepare 

orthophotographs included the capability 

to simultaneously deliver a matrix of 

digital elevations. Developmental work 

is underway in the area of raster scanning of existing map separates and the 

editing and conversion software needed 

to change this raw data into the standard 

data base format.

The third objective, to establish a 

digital cartographic data base suited to 

geographic information systems, also has 

presented a number of problems. Geographic information systems contain 

their own version of the "chicken-andthe-egg" riddle. On the one hand, they 

require preexisting digital cartographic 

data; at the same time, a major part of 

the justification for digitizing maps is

13
to serve large geographic information 

systems. Many current prototype geographic information systems have either 

a deceiving emphasis on color cartographies and marginal quality data or 

else an emphasis on (expensive) customdeveloped thematic data and no link to a 

general-purpose digital cartographic and 

geographic data base. The NMD must anticipate future requirements that are now 

only partially perceived. Considerable 

effort is being devoted to developing 

working relations with other Federal 

agencies having application missions. 

Meanwhile the budgetary process is being 

addressed to secure adequate funding, and 

digital data pricing policy has been put 

into effect. The concept of using the 

facilities and expertise of the NMD to 

provide digitizing and data management 

for other nonbase categories on request 

(a digital service center) is still under 

active consideration.

The fourth and final objective in the 

NMD plan is to reconfigure the conventional mapping process to take full 

advantage of automation. The rapidly increasing capability of all types of computers and automated equipment, coupled 

with decreasing processing costs (more 

bits for the "buck"), makes this a very 

desirable goal especially in light of 

escalating personnel costs. The previously mentioned perspective that led to 

our delay in producing maps digitally is 

less true today. The current NMD mapping 

process as shown in figure 1 is largely 

a linear sequence of operations, all of 

which must be accomplished to produce the 

final product a printed map. Appended 

to the process are several digitizing 

operations that spin off some categories 

of data for the digital cartographic data 

base.

Because the process is sequential, 

any delay in a particular phase field 

survey or acquisition of aerial photography adversely affects all later phases 

and results in excessive time between 

authorization of a map and its appearance 

in printed form. The finality of committing a map (usually a contiguous set of 

maps in a project) to printing requires 

that current information on all data 

categories in a region must be gathered 

concurrently to converge into a set of 

coexisting film separates that have one

primary purpose to print the map. Different data categories, however, have 

vastly different cycles of change, and 

even adjacent maps in an area may have 

varying rates of change. It is often impractical to revise a map until sufficient change has occurred in several 

categories over a sufficient number of 

adjacent maps to justify a project. Then 

all categories must be evaluated in the 

process of focusing on a new printing.

The proposed future mapping process, 

shown in figure 2, emphasizes the digital 

cartographic data base and the independent assemblage of data categories, each 

according to its own requirements for 

currency and by methods most appropriate 

to the category. Boundaries might, for 

example, be encoded from survey records 

without ever being depicted on a map. 

Two results of this revised mapping concept are (1) a greatly decreased emphasis 

on the printed map as the overriding 

reason for gathering cartographic data 

for the archival record and (2) a greatly 

increased flexibility and capability to 

respond to a variety of data requests, 

including conventional base maps but also 

special maps and digital map data. The 

NMD will become a manager of cartographic 

data categories and not merely (as in the 

past) a mapmaker. it is entirely possible that the current practice of printing several thousand copies of every map 

may become obsolete as advances in highspeed, limited-run printing devices and 

electronic displays make the preparation 

and distribution of individually customized maps more viable.

Another effect of emphasizing data 

categories in a data base will be the 

ability to manage a particular category 

according to the full range of its applications and not be constrained by the 

printed representation. Digital elevation data can define contours or can be 

in the form of an array that is more 

suitable for other applications, such as 

in an analysis with Landsat multispectral 

data. Digital elevations also can be extracted from the data base to drive a 

controller on automated orthophoto instruments and thus eliminate the requirement for an operator in the scanning 

operations. The evolution of automated 

cartography seems to lie not so much in 

the area of automating the conventional

14
CURRENT PROCESS

SOURCE SEPARATES

FIELD WORK 

AERIAL « 

PHOTOGRAPHY

PHOTO 

INTERPRETATION

'COMPILATION EDITING!

DEFENSE DIGITAL

MAPPING TERRAIN

AGENCIES MODEL

AERIAL , 

PHOTOGRAPHY

GESTALT PHOTO MAPPER-2, MANUAL PROFILING

AERIAL 

PHOTOGRAPHY

PHOTO 

INTERPRETATION

 MAPPINGOPEN FILE 

MAPS

 DIGITIZING'

 DIGITIZING

O

P

Q

LU

L

LEGEND FOR ABREVIATIONS

OLG DIGITAL LINE GRAPH

DEM DIGITAL ELEVATION MODEL

LU/LC LAND USE/LAND COVER

Figure 1. Current mapping process of the USGS National Mapping Divisi
FUTURE PROCESS

SOURCE DIGITAL CARTOGRAPHIC DATA 

BASE

1 

FIELD

INVESTIGATION

AERIAL 

PHOTOGRAPHY

DIRECT DIGITAL

RECORDING

I .

DATA GENERATED

DV/ tLt A f

MAPPING DIV.

t

USGS 

STANDARDS

4

DATA GENERATED

RV- ATMFD

AGENCIES

NAT. MAPPING 

 M^ DIV QUALITY «^>

CONTROL

OTHER

Figure 2. Proposed future mapping process of the USGS National Mapping D
sequential process but in bringing categories of data into a cartographic and 

geographic data base concept and then 

using the data base for map preparation. 

Some data categories can be developed 

relatively quickly and easily and have 

significant payoffs outside the traditional map. Other categories may be more 

difficult to acquire or may not require 

or justify the additional complexity of 

being structured for the data base. When 

needed on a map, these categories might 

be handled much as at present.

DATA STRUCTURE AND DATA MANAGEMENT

Two major issues that must be solved 

early when dealing with digital cartographic/geographic data are data structuring and data management. Successful 

resolution of these issues is crucial to 

the long-term viability of a national 

data base because, when data are transformed from their graphic (map) representation to a digital form, two things 

occur:

1. The spatial relationships among 

various elements of the data that are 

visually obvious in the graphic form 

can be completely lost if the digital 

encoding is not done with extreme 

care and considerable forethought 

about future applications.

2. The transformation of cartographic/ 

geographic data from a graphic to 

digital representation generates very 

large data volumes that require explicit management strategies to prevent complete chaos in the resulting 

data base.

Taking the first issue, data structuring, the NMD has recognized the 

necessity of developing a data base that 

is topologically structured both for 

automated cartography and for geographical analysis. Topological structuring 

essentially maintains the spatial relationships inherent in the data that are 

usually obvious to the human mind when 

visually examining a. graphic representation of the data. Topology (the mathematical study of the relationships and 

transformations of geometric configurations) as defined for cartography and

automated spatial analysis requires that 

all lines be explicitly linked to nodes 

(ends of lines or line junctions) and all 

areas be explicitly coded to the bounding 

arcs (lines). All nodes, lines, and 

areas are completely and unambiguously 

linked into a completely defined digital 

line graph that can be interpreted in a 

computer environment without resorting to 

human perception and assistance. Maintaining the topology of the data is especially important in applications related 

to geographic information systems. For 

example, in geographic analysis, we want 

to retain the following spatial 

relationships:

1. The coordinate position of a point 

with respect to other data elements 

expressed as points, lines, or areas 

(this includes map projection 

parameters);

2. The shape and size of an area (the 

lines that bound a polygon must be 

linked to each other and to the 

polygon they define);

3. The intersection between points, 

lines, and areas (when a point falls 

within an area, when a line cuts 

through an area, and when two areas 

overlap or intersect);

4. The property of connectivity for 

lines (through a stream network or a 

road system, and so on); and

5. The property of adjacency (when two 

areas share a common boundary).

These relationships have all been 

previously recognized in the literature 

on automated geographical analysis and 

were adopted and developed through the 

USGS Geographic Information Retrieval 

and Analysis System (computer programs 

for land use and land cover analysis) 

(Mitchell, and others, 1977). These same 

relationships, plus others, are just now 

being recognized as equally important to 

automated cartography. Some of the 

cartographic relationships are as 

follows:

1. Coincidence of features. When, for 

example, a road and a boundary occupy 

the same geographical location, this 

must be known through explicit coding 

to appropriately instruct automated 

plotting equipment which feature

17
takes precedence in producing a 

graphic image. Failure to specify 

this would produce a very unpleasing, 

and sometimes unreadable, graphic 

product.

2. Multiple feature coding. Often a 

"line" in digital form has several 

meanings; for example, it symbolizes 

a road with a list of attributes, 

some of which must be translated into 

cartographic symbols. The same line 

may also represent part of a boundary. Once again, the initial encoding of the data must contain the 

relationships necessary for automatic 

plotting equipment to operate efficiently on a variable string of 

attribute codes, such as highway 

type, width, route number, and type 

of boundary.

3. Data generalization. Automated 

cartographic processes allow for 

great flexibility in changing the 

scale of the graphic products. There 

are, however, limits to the amount of 

scale change that can be accomplished 

without serious distortion of the 

data. There is also potential for 

cartographic dishonesty in displaying data at a scale larger than 

warranted by the information content. 

As scales become smaller, certain 

features, because of size or proximity to other features, must be 

deleted from the graphic product. 

Either very intelligent algorithms 

will be needed to automatically 

accomplish such deletions or else 

explicit topological codes must be 

entered into the data to identify 

situations where such adjustments 

must be made.

4. Data ordering. The ordering and 

placement of the data in the file are 

of critical importance for automated 

cartographic operations. Data retrieval, editing, and plotting must 

be optimized for maximum efficiency. 

Interactive editing systems and precision plotters have traditionally 

been rather slow, and, while some 

improvement may be anticipated, a 

file structure that permits efficient 

use of the equipment may be critical 

to the success of an operation.

The DLG and DEM files may be structured in one of three ways, called 

levels:

1. Level 1 This is the simplest 

structure which maintains the 

original (raw) data in a standardized format, coded to prescribed 

standards, and edited for normal 

input errors. The main purpose of 

this level is to meet three needs: 

(1) to provide a source of digital 

data quickly; (2) to provide data to 

users who can complete the structuring process; and (3) to provide 

data for plotting or display systems 

of low or moderate cartographic 

quality.

2. Level 2 This structure is designed 

to support graphic display or plotting equipment of high cartographic 

quality. The DLG files contain extensive attribute codes that describe 

the graphic elements. The DEM files 

are enhanced for consistency and 

filtered to reduce data volume.

3. Level 3 The third structure is 

used for fully topologically structured data files designed to be integrated into geographic information 

systems. All topological relationships have been defined for the DLG 

data, and the DEM data have been 

modified to be consistent with the 

corresponding planimetric data 

(represented by the DLG data file).

These three levels do not easily 

aggregate in an upward direction. Data 

collected under criteria and specifications for level 1 or level 2 cannot 

always be enhanced to level 3, and, to 

achieve this level, it is often easier 

and more cost effective to recapture the 

data in level 3 form. However, the 

reverse process of extracting level 2 

from level 3 data, or level 1 from level 

2, is more easily accomplished. This 

fact is of profound importance in planning data acquisition with a view toward 

future requirements.

The second issue, data management, is 

crucial because of the large data volumes 

generated from graphic products and because automated systems are storing

18
two- or three-dimensional data in a onedimensional storage medium (sequential 

bits on a computer tape or disk). Such 

issues as how to efficiently partition 

the data base to serve multiple uses, how 

to reassemble it on demand, and how to 

maintain quality control as the data base 

is built and maintained over long periods 

must be resolved. Another insidious 

problem is that cartographic data in a 

computer environment are woefully nonvisible? that is, an error that would be 

perfectly obvious to the eye may not be 

recognized by the computer and may remain 

hidden for a long time. Some errors or 

incompatibilities defy attempts to develop automated logic checks short of extremely extensive and expensive qualitycontrol measures.

Finally, an unsolved problem in automated cartography centers around automatic name placement (Goldberg and Miller, 

1983). The USGS Geographic Names Information System contains most of the name 

information needed for automated map production if the placement problem can be 

solved. It may be that certain data relationships or structures can be entered 

when the spatial data are encoded that 

could facilitate the automatic placement 

of some or all of the name information 

required on a map.

CONCLUSION

These are the accomplishments, perspectives, and concerns of the NMD as we 

move into the development of a national 

digital cartographic/geographic data 

base. We have not completely solved all 

issues, but we believe we have made good 

progress to date. We currently are encoding and storing our data in a way to 

minimize data loss and thereby maximize 

future use of the data. However, all of 

these future uses have yet to emerge* We 

are therefore progressing step by step 

and attempting to assess all the implications of any particular action or design 

feature of this data base. The complete 

transition to achieve all of our objectives and reconfigure the mapping process 

is anticipated to take most of this 

decade and even beyond. However, the NMD 

is firmly committed and will increasingly

become the manager of the national 

digital cartographic data categories 

through sophisticated data base management systems.

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