A digital elevation model (DEM) is a digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals. The USGS produces five different digital elevation products. 1-Degree DEMs correspond to the 3 arc-second – 3- x 3-arc-second data spacing – (or 1:250,000-scale) USGS topographic map series, and are available for all of the contiguous U.S. and most of Alaska.
They are expressed in geographic coordinates (latitude/longitude). Most are referenced to the World Geodetic Survey (WGS) system of 1972 (WGS72), but some are referenced to the WGS system of 1984 (WGS84). Grid spacing is 3 arc-seconds.
To download FREE 1:250K USGS DEM data, please select a State on the map below.
Files are available in Native format and are distributed via FTP download (see http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html)