The National Elevation Dataset (NED) is a new raster product assembled by the U.S. Geological Survey. The NED is a seamless mosaic of best-available elevation data with a consistent datum, elevation unit, and projection. Data corrections were made in the NED assembly process to minimize artifacts, perform edge matching, and fill sliver areas of missing data. One of the effects of the NED processing steps is a much-improved base of elevation data for calculating slope and hydrologic derivatives. Older DEM's produced by methods that are now obsolete are filtered during the NED assembly process to minimize artifacts that are commonly found in data produced by these methods. NED processing also includes steps to adjust values where adjacent DEM's do not match well, and to fill sliver areas of missing data between DEM's. These processing steps ensure that NED has no void areas and artificial discontinuities have been minimized. In cases where 7.5-minute DEM's have 10-meter resolution, the original source data will be at a higher resolution than the NED. In 1999 the Canaan Valley Institute and WVGISTC published the ERDAS IMAGINE mosaic. In 2002 the WV DEP published an ArcGrid mosaic that eliminated the noise artifact associated with hillshaded images. The WV DEP elevation grid was merged into a single block, reprojected using bilinear interpolation to a 30M cell size and cropped using a state boundary grid that was buffered outward 1km. The WV DEP elevation grid data was then rounded to the nearest integer value to reduce the file size.