A Digital Line Graph (DLG) is a

cartographic Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an im ...

map feature represented in digital

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

form that is distributed by the

U.S. Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and ...

(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, or SDTS, is a standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventio ...

(SDTS) format and are topologically structured for use in mapping and

geographic information system A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...

(GIS) applications.

Description

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 Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

and 1:30,000-scale for

Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...

; 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 The ''National Atlas of the United States'' was an atlas published by the United States Department of the Interior from 1874 to 1997. Older editions were printed, but the most recent edition was available online. Since it is a publication of t ...

. Large-scale DLGs are usually cast on the

Universal Transverse Mercator coordinate system The Universal Transverse Mercator (UTM) is a map projection system for assigning coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal position representation, which means i ...

(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 The Albers equal-area conic projection, or Albers projection (named after Heinrich C. Albers), is a conic, equal area map projection that uses two standard parallels. Although scale and shape are not preserved, distortion is minimal between t ...

system or the

geographic coordinate system The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various ...

latitude and longitude The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various ...

, depending on the distribution format. All DLGs are referenced to the

North American Datum The North American Datum (NAD) is the horizontal datum now used to define the geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In surveying, ca ...

of 1927 (NAD27) or the North American Datum of 1983 (NAD83). USGS DLGs are topologically structured for use in mapping and

(GIS) applications.

Data categories

Nine different categories of features, or layers, are available in DLGs:

Public Land Survey System The Public Land Survey System (PLSS) is the surveying method developed and used in the United States to plat, or divide, real property for sale and settling. Also known as the Rectangular Survey System, it was created by the Land Ordinance of 1 ...

(PLSS), Boundaries (BD), Transportation (TR),

Hydrography Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary p ...

(HY),

Hypsography Hypsometry () is the measurement of the elevation and depth of features of the Earth's surface relative to mean sea level. On Earth, the elevations can take on either positive or negative (below sea level) values. The distribution is theorised ...

(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 In mathematics, topology (from the Greek language, Greek words , and ) is concerned with the properties of a mathematical object, geometric object that are preserved under Continuous function, continuous Deformation theory, deformations, such ...

linkages contained in line, node and area elements; and

(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.USGS Fact Sheet, Digital Line Graphs
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References

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External links

USGS Digital Line GraphsUSGS Product GuidesNational Atlas home page''The National Map''
Cartography United States Geological Survey GIS vector file formats