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Data > GISDataDepot DEMs > About Data
> Click here for important information regarding DEMs.





USGS Nationwide 250K DEM Bundle
GeoCommunity

Your Price: $69.95



All Available USGS 1:250K DEMs delivered on CD.

BACKGROUND INFORMATION
A digital elevation model (DEM) consists of an array of elevations for ground positions that are usually at regularly spaced intervals.

The 1-degree DEM provides coverage in 1- by 1-degree blocks and is available for all of the contiguous United States, Hawaii, and most of Alaska. The basic elevation model is produced by the Defense Mapping Agency (DMA) using cartographic and photographic sources.

The 1-degree DEM consists of a regular array of elevations referenced horizontally on the geographic coordinate (latitude/longitude) system of the World Geodetic System 1984 Datum. Elevation data located on the degree lines (all four sides) correspond with the same profiles on adjoining DEM blocks.

Elevations are in meters relative to mean sea level. Spacing of the elevations along and between each profile is 3 arc-seconds with 1,201 elevations per profile. The only exception are DEMs in Alaska, where the spacing and number of elevations per profile varies depending on the latitudinal location of the DEM. Latitudes between 50 and 70 degrees north have spacings at 6 arc-seconds with 601 elevations per profile and latitudes greater than 70 degrees north have spacings at 9 arc-seconds with 401 elevations per profile.

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