Historic Digital Elevation Models (DEMs)
Product Description The United States Geological Survey (USGS) maintains a large inventory of elevation data produced from source maps and photographs of varying vintage. Digital Elevation Models (DEMs) from older sources have the potential to describe an historic land surface. This product consists of nearly 13,000 discrete, native format USGS DEMs, which would otherwise be unavailable. Criteria Typically, there are several DEMs available per quadrangle area. For this product, the best of the oldest DEMs are selected. Only better "level 2" data are selected with the notable exception of a pre-eruption DEM of Mount St. Helens, WA, which was produced by the manual profiling technique. A select historic DEM may be as little as one year older than a more current version of the same DEM. The specific DEMs chosen reflect current inventory, and is subject to change. Caveats Unlike DEMs used to populate the National Elevation Dataset, these DEMs have not been reviewed for quality, and have not been subjected to corrective filtering or edge matching. They may on occasion exhibit spurious values or may be coded in incorrect units. Further, DEMs with older source dates may show little difference in content. More often, only a quality difference is observed. These data are provided on speculation of historic content only. Contact Us For further assistance or to obtain data, please contact:
webmapping@usgs.gov |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://ned.usgs.gov
Page Contact Information: webmapping@usgs.gov
Page Last Modified: August 2006
