Digital line graph
Encyclopedia
A Digital Line Graph is a cartographic
map feature represented in digital vector
form that is distributed by the U.S. Geological Survey (USGS). DLGs are collected from USGS maps and are distributed in large-, intermediate- and small-scale with up to nine different categories of features, depending on the scale. They come in optional and Spatial Data Transfer Standard
(SDTS) format and are topologically structured for use in mapping and geographic information system
(GIS) applications
DLGs are normally derived from USGS maps or USGS map-related sources. DLGs are distributed at three different scales: large-scale, which normally correspond to the USGS 7.5- by 7.5-minute, 1:24,000 and 1:25,000-scale topographic quadrangle map series, 1:63,360-scale for Alaska
and 1:30,000-scale for Puerto Rico
; intermediate scale, which are derived from the USGS 30- by 60-minute, 1:100,000-scale map series; and small-scale, which are derived from the USGS 1:2,000,000-scale sectional maps of the National Atlas of the United States
. Large-scale DLGs are usually cast on the Universal Transverse Mercator coordinate system
(UTM), but are sometimes cast on the State Plane rectangular coordinate system. Intermediate-scale DLGs are sold in 30- by 30-minute sections that correspond to the east or west half of the 100K quadrangle map, and each of the 30-minute sections is distributed in four 15- by 15-minute cells and is cast on the UTM coordinate system. Small-scale DLGs are sold in state units and are cast on either the Albers equal-area conic projection system or the geographic coordinate system
of latitude and longitude, depending on the distribution format. All DLGs are referenced to the North American Datum
of 1927 (NAD27) or the North American Datum of 1983 (NAD83). USGS DLGs are topologically structured
for use in mapping and geographic information system
(GIS) applications.
(PLSS), Boundaries (BD), Transportation (TR), Hydrography
(HY), Hypsography (HP), Non-vegetative features (NV), Survey control and markers (SM), Man-made features (MS) and Vegetative surface cover (SC). Large-scale DLGs offer all nine layers, while intermediate-scale DLGs offer the five layers of PLSS, BD, TR, HY and HP. Small-scale DLGs offer the five layers of PLSS, BD, TR, HY and MS.
(SDTS) format, a format that facilitates transferring of spatial data between different computer systems.
Large-scale DLGs are available in optional format and will also be available in SDTS format as the data from each state is converted. Intermediate-scale DLGs are available in optional format and the HY and TR layers are also available in SDTS format. Small-scale DLGs are available in both optional and SDTS formats.
Cartography
Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...
map feature represented in digital vector
Vector graphics
Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
form that is distributed by the U.S. Geological Survey (USGS). DLGs are collected from USGS maps and are distributed in large-, intermediate- and small-scale with up to nine different categories of features, depending on the scale. They come in optional and Spatial Data Transfer Standard
Spatial Data Transfer Standard
Spatial Data Transfer Standard, or SDTS, is a standard used to describe earth-referenced spatial data. It was designed to easily transfer and use spatial data on different computer platforms.-External links:* ** *...
(SDTS) format and are topologically structured for use in mapping and geographic information system
Geographic Information System
A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...
(GIS) applications
Description
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and 1:30,000-scale for Puerto Rico
Puerto Rico
Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...
; intermediate scale, which are derived from the USGS 30- by 60-minute, 1:100,000-scale map series; and small-scale, which are derived from the USGS 1:2,000,000-scale sectional maps of the National Atlas of the United States
National Atlas of the United States
The National Atlas of the United States is an online atlas published by the United States Department of the Interior.Since it is a publication of the United States Government, the atlas and the maps contained therein are in the public domain....
. Large-scale DLGs are usually cast on the Universal Transverse Mercator coordinate system
Universal Transverse Mercator coordinate system
The Universal Transverse Mercator geographic coordinate system uses a 2-dimensional Cartesian coordinate system to give locations on the surface of the Earth. It is a horizontal position representation, i.e...
(UTM), but are sometimes cast on the State Plane rectangular coordinate system. Intermediate-scale DLGs are sold in 30- by 30-minute sections that correspond to the east or west half of the 100K quadrangle map, and each of the 30-minute sections is distributed in four 15- by 15-minute cells and is cast on the UTM coordinate system. Small-scale DLGs are sold in state units and are cast on either the Albers equal-area conic projection system or the geographic coordinate system
Geographic coordinate system
A geographic coordinate system is a coordinate system that enables every location on the Earth to be specified by a set of numbers. The coordinates are often chosen such that one of the numbers represent vertical position, and two or three of the numbers represent horizontal position...
of latitude and longitude, depending on the distribution format. All DLGs are referenced to the North American Datum
North American Datum
The North American Datum is the official datum used for the primary geodetic network in North America.In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 and the North American Datum of 1983...
of 1927 (NAD27) or the North American Datum of 1983 (NAD83). USGS DLGs are topologically structured
Topological space
Topological spaces are mathematical structures that allow the formal definition of concepts such as convergence, connectedness, and continuity. They appear in virtually every branch of modern mathematics and are a central unifying notion...
for use in mapping and geographic information system
Geographic Information System
A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...
(GIS) applications.
Data Categories
Nine different categories of features, or layers, are available in DLGs: Public Land Survey SystemPublic Land Survey System
The Public Land Survey System is a method used in the United States to survey and identify land parcels, particularly for titles and deeds of rural, wild or undeveloped land. Its basic units of area are the township and section. It is sometimes referred to as the rectangular survey system,...
(PLSS), Boundaries (BD), Transportation (TR), Hydrography
Hydrography
Hydrography is the measurement of the depths, the tides and currents of a body of water and establishment of the sea, river or lake bed topography and morphology. Normally and historically for the purpose of charting a body of water for the safe navigation of shipping...
(HY), Hypsography (HP), Non-vegetative features (NV), Survey control and markers (SM), Man-made features (MS) and Vegetative surface cover (SC). Large-scale DLGs offer all nine layers, while intermediate-scale DLGs offer the five layers of PLSS, BD, TR, HY and HP. Small-scale DLGs offer the five layers of PLSS, BD, TR, HY and MS.
Distribution Formats
DLGs are available in two different formats: optional format, a simple-to-use format that incorporates an 80-byte logical record length, the UTM ground coordinate system, and topology linkages contained in line, node and area elements; and Spatial Data Transfer StandardSpatial Data Transfer Standard
Spatial Data Transfer Standard, or SDTS, is a standard used to describe earth-referenced spatial data. It was designed to easily transfer and use spatial data on different computer platforms.-External links:* ** *...
(SDTS) format, a format that facilitates transferring of spatial data between different computer systems.
Large-scale DLGs are available in optional format and will also be available in SDTS format as the data from each state is converted. Intermediate-scale DLGs are available in optional format and the HY and TR layers are also available in SDTS format. Small-scale DLGs are available in both optional and SDTS formats.