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|USGS Nationwide 250K DEM Bundle|
Your Price: $69.95
All Available USGS 1:250K DEMs delivered on CD.
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.