Digital Line Graphs Data Layer
Digital Line Graphs are digital representations of the features
displayed on a U.S. Geological Survey topographic map. DLGs are
provided by the USGS in numerous scales of which 1:24,000 and 1:100,000
are the most commonly used. Several descriptive attributes are
contained such as feature type and feature name, that facilitate DLG
Digital Line Graph Directories:
cty County Boundaries
for Forests Boundaries
mun Municipalities Boundaries
prk Parks Boundaries
ptl Power and Transmission Lines
ref Refuges Boundaries
res Reservations Boundaries
wma Wildlife Management Areas Boundaries
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 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 orthophotoquadrangle 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 UnitedStates 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 degrees
N., cover 15- by 20-minute areas; between 59 and 62degrees N., 15- by
22.5-minute areas; between 62 and 68 degrees 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
verticalpositions (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 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 areused, 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
Intermediate-scale hydrography and transportation DLG's are sold on
compact disc-read only memory (CD-ROM). Each disc contains all the 15-
by 15-minute cells within the 1:100,000-scale quadranglesthat 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 available in five categories or
units: (1) Public Land Survey System; (2) boundaries; (3)
ransportation; (4) hydrography; and (5) hypsography.
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.
VirginIslands, and Alaska will be revised by the end of 1996.
Small-scale DLG's are available in five categories or units: (1)
boundaries; (2) transportation, including roads and trails, railroads,
pipelines, and airports; (3) hydrography; (4) manmade features,
including built-upareas, 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.
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
elementbelongs, 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
attributecode, 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
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 intermediate-scale 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-scaleDLG'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
United States Geological Survey (USGS)
Earth Science Information Center