1. GTOPO30 Global 30-arc-second (1-km) elevation model - “Best available” global DEM - Initial release: March 1997 - Widely used for climate modeling, land cover characterization, hydrologic modeling, and EOS satellite image product generation - Seamless raster data derived from multiple source datasets - GTOPO30 continues to be a very popular product, averaging over 12,000 files downloaded each month

2. The National Elevation Dataset (NED) Seamless national coverage of “best available” raster elevation data –Geographic “projection” –1-arc-second (30-meter), 1/3-arc-second (10-meter), and 1/9-arc-second (3-meter) grid spacing Alaska: 2-arc-second grid spacing –Datum: NAD 83 horizontal; NAVD 88 vertical –Elevation units: decimal meters –Updated bi-monthly to incorporate all new USGS DEM production and other newly available source data NED is the elevation layer of The National Map

3. National Elevation Dataset: Source Data April 2007 release: over 70% 10-meter DEM source or better 3 meters or better (3%) 10 meters or better (67%) 30 meters (30 %) Source Data Resolution

4. Shuttle Radar Topography Mission Data Distribution