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Title of Listing:
|Digital Elevation Models (DEMs)|
|US Geological Survey-USGS, All Listings|
Digital records of terrain elevations for ground positions at regularly spaced horizontal intervals which are derived from United States Geological Survey (USGS) 7.5-minute, 15-minute, 30 by 60-minute, and 1-degree (1:250,000-scale) quadrangle map by hypsographic data and/or photogrammetric methods.
Elevation data spacing varies from 30 meters for 7.5-minute DEMs to 3 arc seconds for 1:250,000 scale maps. Complete U.S. coverage is only available for the 1:250,000-scale digital line graph (DLG) data. All DEM data are similar in logical data structure and are ordered from south to north in profiles that are ordered from west to east.
7.5-minute DEM data are produced in 7.5-minute units which correspond to USGS 7.5-minute topographic quadrangle map series. 7.5-minute DEM data consist of a regular array of elevations referenced horizontally on the Universal Transverse Mercator (UTM) coordinate system of the North American Datum of 1927 (NAD 27). These data are stored as profiles with 30-meter spacing along and between each profile.
15-minute DEM data correspond to USGS 15-minute topographic quadrangle map series in Alaska. The unit sizes in Alaska vary depending on the latitudinal location of the unit. 15-minute DEM data consist of a regular array of elevation referenced horizontally to the geographic (latitude/longitude) coordinate system of North American Datum 1927 (NAD 27). The spacing between elevations along profiles is 2 arc seconds of latitude by 3 arc seconds of longitude.
30-minute DEM data cover 30-minute by 30-minute areas which correspond to the east half or west half of the USGS 30- by 60-minute topographic quadrangle map series for the conterminous United States and Hawaii. Each 30-minute unit is produced and distributed as four 15- by 15-minute cells. 30-minute DEM data have the same characteristics as the 15-minute DEM data except that the spacing of elevations along and between each profile is 2 arc seconds.
1-degree DEM data are produced by the Defense Mapping Agency in 1-degree by 1-degree units which correspond to the east half or west half of USGS 1- by 2- degree topographic quadrangle maps series, for all the United States and its territories. 1-degree DEM data consist of a regular array of elevations referenced horizontally using the geographic (latitude/longitude) coordinate system of the World Geodetic System 1972 Datum. A few units are also available using the World Geodetic System 1984 Datum. Spacing of the elevations along and between each profile is 3 arc seconds with 1,201 elevations per profile. The only exception is DEM data in Alaska, where the spacing and number of elevations per profile varies depending on the latitudinal location of the DEM.
USGS Information Services accepts fax and mail orders only.
Visit the USGS at http://edcwww.cr.usgs.gov/webglis or http://mapping.usgs.gov
|US Department of the Interior (DOI), US Geological Survey (USGS)|
|Denver ||Information Services ||(800) 435-7627 |
|Earth Science Information Center||(800) 872-6277 |
|EROS Data Center||(605) 594-6151 |
|United States |
|Fax:|| Information Services (303) 202-4693|