The U.S. Geological Survey has developed a National Elevation Database (NED). The NED is a seamless mosaic of best-available elevation data. The 7.5-minute elevation data for the conterminous United States are the primary initial source data. In addition to the availability of complete 7.5-minute data, efficient processing methods were developed to filter production artifacts in the existing data, convert to the NAD83 datum, edge-match, and fill slivers of missing data at quadrangle seams. One of the effects of the NED processing steps is a much-improved base of elevation data for calculating slope and hydrologic derivatives.
The USDA Natural Resources Conservation Service has taken this data from Geographic projection, NAD83, and converted it into UTM, NAD83. NED has been tiled into one degree blocks and remains seamless from one degree east and one degree west of any UTM zone break. Included within any gzip file is the ArcInfo elevation grid, ArcView metadata shapefile, enhanced 10-meter shaded relief as a bil image, and the 10-meter shaded relief in tif format.
After reprojection, the mosaic was clipped using the extents of the reprojected ArcInfo coverage, thereby creating a full one degree block without any null data areas. This allows the clipped elevation grid to be seamless with adjacent clipped NED blocks that have been processed in this way. After clipping the elevation grid, a shaded relief was created using the default settings in ArcInfo. The shaded relief was then converted into a tif image. A new field was created in the polygon attribute table called "NRCSDATE" that provides the date at which the NED tile was processed at the National Cartography & Geospatial Center. The metadata coverage was then converted into an ESRI ArcView shapefile.
The elevation grid and shaded relief grid were merged into one grid, thereby creating a new enhanced grid to highlight elevation differences. This enhanced grid was resampled to 10-meters and converted to integer values. It was then converted into a grid stack before creating a shaded relief bil image. This new enhanced 10-meter bil image allows for a larger map scale then would be available with the 30-meter shaded relief tif. The drawback is the much larger file size of the 10-meter bil.
Finally, each one degree block folder with contents including the elevation ArcInfo grid, metadata ArcView shapefile, enhanced 10-meter shaded relief bil, and 30-meter tif shaded relief was then tarred and gzipped.
ArcView Shapefile - Three File Types: .dbf. shp. shx
Shaded Relief - bil, hdr, stx, prj, and blw
Shaded Relief - tif and tfw files
ned_metadata.xml ned_metadata.html ned_readme.txt USGS_NED_factsheet.pdf
Softcopy in Adobe Acrobat Portable Document File (PDF) format: <http://rockyweb.cr.usgs.gov/nmpstds/demstds.html>