Digital Line Graph Data

Digital line graph (DLG) data are digital

representations of cartographic information. DLG’s of map features are digital

vectors converted from maps and related

sources. The U.S. Geological Survey

(USGS) DLG data are classified as large,

intermediate, and small scale.

Data Sources, File

Content, and File Extent

Large-Scale DLG’s

Large-scale DLG’s are derived from the

USGS 1:20,000-, 1:24,000-, and

1:25,000-scale 7.5-minute topographic

quadrangle maps. When large-scale

DLG’s are revised, a recent digital

orthophoto quadrangle is usually used 

to update those categories of DLG data

that can be detected from an aerial

photograph.

Large-scale DLG’s are produced in 

7.5-minute units that correspond to

USGS 1:20,000-, 1:24,000-, and

1:25,000-scale topographic quadrangle

maps. However, some older units in the

Western United States cover 15-minute

areas and correspond to maps at 1:62,500

scale. The unit sizes in Alaska vary

depending on latitude. Units south of 

59° N., cover 15- by 20-minute areas;

between 59° and 62° N., 15- by

22.5-minute areas; between 62° and 

68° N., 15- by 35-minute areas (all

values are latitude and longitude,

respectively).

Large-scale DLG’s are available in nine

categories or units: (1) Public Land

Survey System, including township,

range, and section line information; 

(2) boundaries, including State, county,

city, and other national and State lands

such as forests and parks; (3) transportation, including roads and trails, railroads, pipelines, and transmission lines;

(4) hydrography, including flowing

water, standing water, and wetlands; 

(5) hypsography, including contours and

supplementary spot elevations; (6) nonvegetative features, including lava, sand,

and gravel; (7) survey control and

markers, including horizontal and

vertical positions (third order or better);

(8) manmade features, including cultural

features not collected in other data

categories such as buildings; and 

(9) vegetative surface cover, including

woods, scrub, orchards, vineyards, and

vegetative features associated with

wetlands.

All nonstandard quadrangles with neatlines that extend beyond the standard unit

size to accommodate overedge boundaries are collected as multiples of the

standard unit size. Data covering a 7.5-

by 8.5-minute area would, therefore, be

sold as two 7.5-minute units. 

Intermediate-Scale DLG’s

Intermediate-scale DLG’s are derived

from USGS 1:100,000-scale 30- by 60-

minute quadrangle maps. If these maps

are not available, Bureau of Land

Management planimetric maps at

1:100,000 scale are used, followed by

archival compilation materials.

Intermediate-scale DLG’s are sold in 30-

by 30-minute units that correspond to the

east or west half of USGS 30- by 60-

minute 1:100,000-scale topographic

quadrangle maps. Each 30-minute unit is

produced and distributed as four 15- by

15-minute cells, except in high-density

areas, where the 15-minute cells may be

divided into four 7.5-minute cells.

Intermediate-scale hydrography and

transportation DLG’s are sold on

compact disc-read only memory (CDROM). Each disc contains all the 15- by

15-minute cells within the 1:100,000-

scale quadrangles that cover a State or

States. Fourteen sectional regions in the

United States covering the conterminous

48 States and Hawaii are available.

Presently, intermediate-scale DLG’s are

sold in five categories or units: (1) Public

Land Survey System; (2) boundaries; 

(3) transportation; (4) hydrography; and

(5) hypsography.

Small-Scale DLG’s

Small-scale DLG’s are derived from the

USGS 1:2,000,000-scale sectional maps

of the National Atlas of the United States

of America. Small-scale DLG’s were

revised from 1990-95 sources.

Small-scale DLG’s are sold in State

units. At present, the 48 conterminous

States and Hawaii have been revised.

The District of Columbia is contained

within the Maryland unit. Puerto Rico,

the U.S. Virgin Islands, and Alaska will

be revised by the end of 1996.

Small-scale DLG’s are available on two

types of CD-ROM discs. One disc type

contains data in DLG Optional (DLG-O)

format. The other disc type contains

DLG-O data in the Spatial Data Transfer

Standard (SDTS) format. Each CD-ROM

disc contains small-scale DLG’s for 49

States and the District of Columbia.

Small-scale DLG’s are sold in five

categories or units: (1) boundaries; 

(2) transportation, including roads and

trails, railroads, pipelines, and airports;

(3) hydrography; (4) manmade features,

including built-up areas, capitals, county

seats, populated places, and population

range; and (5) Public Land Survey

System, including land grants, township,

range, and subdivisions of the public

lands. 

In addition to the small-scale DLG’s, this

discs contains two associated data files in

ASCII format for each State; these

numbers contain airport names,

populated place names, and population

density. There are also two national files.

One contains land grant names and 

identifiers for the entire United States. 

U.S. Department of the Interior

U.S. Geological Survey US GeoData

Digital Line Graphs

Fact Sheet
The other file contains the Federal

Information Processing Standards’ fivedigit codes for all States, State equivalents, counties, and county equivalents.

Records in these data files can be

associated with cartographic features

contained in the small-scale DLG files.

Attribute Codes

Attribute codes are used with vector data

to describe the physical and cultural

characteristics of node, line, and area

elements. Each attribute code identifies

the major category or unit to which a

data element belongs, as well as the

specific nature of the element. Codes

also may provide additional descriptive

information, numerical values, or identifiers. Many elements are uniquely

described by a single attribute code, but

some may require two or more codes for

a complete description. Allowing for a

variable number of attribute codes

creates an open-ended structure to which

information can be added at any time. It

is not necessary for each element to have

associated attributes; in general, attribute

codes are not assigned to an element if

the attributes can be derived on the basis

of relationships to adjacent elements.

Data Distribution Formats

Large-scale DLG’s are available in

optional format. The optional format is

easy to use with an 80-byte logical

record length, a ground planimetric

coordinate system (Universal Transverse

Mercator), and topological linkages

contained in node, line, and area

elements. Large-scale DLG’s will also be

available in the Spatial Data Transfer

Standard (SDTS) format as each State’s

data are converted.

Intermediate-scale DLG’s are available in

optional format. The hydrography and

transportation categories of intermediatescale DLG’s are also available in the

SDTS format. All categories of intermediate-scale DLG’s are available in

SDTS format.

Small-scale DLG’s are available in

optional and SDTS formats. Small-scale

DLG’s in optional format use the ground

planimetric coordinate system of the

Albers Equal-Area Conic projection.

Small-scale DLG’s in SDTS format use

the geographic coordinate system of

latitude and longitude.

Spatial Data Transfer

Standard

The SDTS is a mechanism for

transferring of spatial data between

dissimilar computer systems. The SDTS

specifies exchange constructs, addressing

formats, structure, and content for

spatially referenced vector and raster

data. Advantages of the SDTS include

data and cost sharing, flexibility, and

improved quality, all with no loss of

information.

At present, only ARC/INFO Version 7

from Environmental Systems Research

Institute, Inc., of Redlands, Calif.,

includes an SDTS vector translator.

Other vendors of geographic information

systems (GIS) software are developing

SDTS translators.

Data Records

The optional format classifies data into

eleven record types. For descriptions of

these record types, refer to Data Users

Guide 1, “Digital Line Graphs from

1:24,000-Scale Maps;” Data Users Guide

2, “Digital Line Graph Data from

1:100,000-Scale Maps;” and Data Users

Guide 3, “Digital Line Graphs from

1:2,000,000-Scale Maps.”

SDTS transfers adhere to the Topological

Vector Profile (TVP). A profile is a

clearly defined and limited subset of the

SDTS, designed for use with a specific

type of data. The most effective way to

use the SDTS is to first define a profile;

encoding and decoding software can then

be designed to handle only the options in

that profile. Each small-scale transfer

contains 16 modules defined by the TVP,

which contain information about the

original DLG-O data, including lineage,

completeness, logical consistency, and

spatial domain. Each TVP transfer

includes a varying number of attribute

primary modules, which contain the

attributes of spatial objects. The structure, number, and name of attribute

primary modules will vary with the

DLG-3 theme being transferred.

A master data dictionary is included with

each order of small-scale DLG’s in the

SDTS format. The master data dictionary

contains three modules that identify the

features and attributes of all small-scale

DLG’s.

Data Accuracy and

Verification

DLG’s do not carry quantified accuracy

statements. However, the data files are

checked and validated for file fidelity,

completeness, attribute accuracy,

topological fidelity, and matching edges

before they are released for distribution.

Ordering Information

DLG’s are written as ANSI-standard

ASCII characters in fixed-block format

on unlabeled or ANSI-labeled tape

media. All DLG’s are available for 

a cost on 8-millimeter tape, 3,480

cartridge tape, and compact disc-readable

(CD-R). The data are priced per category

or unit purchased.

To assist you in ordering, the Earth

Science Information Center (ESIC) can

furnish indexes and price list order

forms. Data user guides are included

with all orders except those for the smallscale CD-ROM’s. The data user guide is

included on these CD-ROM’s in ASCII,

Acrobat, PostScript, and WordPerfect 5.1

formats. US GeoData users guides can be

accessed via:

<URL: http://www-nmd.usgs.gov/www/

html/2nmpgds.html>

The files can be downloaded from the

USGS National Mapping Division

Information Server anonymous FTP site:

<URL: ftp://www-nmd.usgs.gov/pub/ti/>

The USGS offers certain US GeoData

data products through the Internet. They

can be retrieved at no cost using

anonymous FTP or World Wide Web

(WWW).

The DLG data bases and their directory

paths are listed below:

- 1:2,000,000-scale DLG’s

(/pub/data/DLG/2M)

- 1:100,000-scale DLG’s

(/pub/data/DLG/100K)
A part of the Washington West, D.C., 1:24,000-scale quadrangle. A part of the Washington West, D.C., 1:24,000-scale DLG showing transportation.

A part of the Washington West, D.C., 1:24,000-scale DLG showing hypsography

(terrain relief).

A part of the Washington West, D.C., 1:24,000-scale DLG showing cultural

features.
To download files using FTP, follow

these steps:

At the prompt, enter ftp and the

following Internet address:

edcftp.cr.usgs.gov

(example: ftp edcftp.cr.usgs.gov)

For “Name” enter “anonymous.”

For “Password” enter your e-mail

address.

Change to the directory containing the

desired files by entering “cd” and the 

directory path specified above for that

particular DLG data base (for example,

to get to the small-scale DLG’s, enter cd

pub/data/DLG/2M).

Enter “ls” to list the files. Locate the

desired quadrangle file. The files are

listed by area name, generally in an

alphabetical list where, for example, the

Austin, Texas, quadrangle would be

found under the directory “A.” SDTS

transfers of 1:2,000,000-scale DLG’s for

Wisconsin would be found under the

directory “W.”

You would enter “cd A” and then “ls” to

see all quadrangle files that begin with

the letter A.

When the desired DLG file has been

located, set the file transfer mode to

binary by entering “binary” at the

prompt. Then enter “get” and the DLG

file name. US GeoData files can also be

retrieved through a USGS WWW server

using browse tools, such as Mosaic. To

use such graphical interfaces, follow

these steps:

Under the file option, open the following

address for the USGS EROS Data Center

home page:

<URL: http://edcwww.cr.usgs.gov/

eros-home.html>

Click on “US GeoData available via

FTP.” Each of the data bases can be

navigated in one or more of the

following ways: alphabetically, by State,

and through a graphical index.

Choose a method of navigation by

clicking on that option. Then locate the

desired DLG file.

Under the options menu, turn on the

“Load to local disc” option.

Click on the file to be downloaded.

Ordering

For further information, contact:

USGS

Earth Science Information Center

507 National Center

Reston, Virginia 20192

1-800-USA-MAPS

For information on other USGS products

and services, call 1-800-USA-MAPS,

e-mail esicmail@usgs.gov, or fax 

703-648-5548.

Receive information from the

EARTHFAX fax-on-demand system,

which is available 24 hours a day at 703-

648-4888.

The address for the USGS home page is

<URL: http://www.usgs.gov/>

Any use of trade, product, or firm names is for

descriptive purposes only and does not imply

endorsement by the U.S. Government.

November 1996 FS-078-96