What is NED DEM data?

Better than 7 1/2 minute quads as we have known them!

Reprocessed to remove the noise present in many old quads.

Currently we have this new elevation data for the Wildcat Creek Watershed:

	NED data - coordinates in longitude latitude! ( NAD83 Geographic) Elevations in decimal meters! This elevation data is present as an ARCGRID or as a /.bil image. [ grid1 ] [ grid 2 ] [ grid 3 ] [ grid 4 ] [ grid 5 ] [ grid 6 ] [ image 1 ] [ image 2 ] [ image 3 ] [ image 4]
	This data is available from the USGS as a seamless grid on CD-ROMs ( for a cost) or for free in 10 megabyte sections (each colored block on the map is a 10 megabyte section)

ALl following is a QUOTE from USGS page at http://edcnts12.cr.usgs.gov/ned/About.htm

NATIONAL ELEVATION DATASET

The National Elevation Dataset (NED) is a new raster product assembled by the U.S. Geological Survey. NED is designed to provide National elevation data in a seamless form 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. NED has a resolution of one arc-second (approximately 30 meters) for the conterminous United States, Hawaii, and Puerto Rico and a resolution of two arc-seconds for Alaska.

NED data sources have a variety of elevation units, horizontal datums, and map projections. In the NED assembly process the elevation values are converted to decimal meters as a consistent unit of measure, NAD83 is consistently used as horizontal datum, and all the data are recast in a geographic projection. Older DEM's produced by methods that are now obsolete have been filtered during the NED assembly process to minimize artifacts that are commonly found in data produced by these methods. Artifact removal greatly improves the quality of the slope, shaded-relief, and synthetic drainage information that can be derived from the elevation data. Figure 2 illustrates the results of this artifact removal filtering. 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.

Figure 2. A shaded-relief representation of the Rockypoint, Wyoming 7.5-minute DEM is shown above on the left. The same area is shown on the right after NED artifact filtering has been performed. The super-imposed red lines are synthetic drainage networks derived from each elevation dataset. 

As higher-resolution or higher-quality data become available, the NED is periodically updated to incorporate best-available coverage. As USGS's 7.5-minute and 15-minute digital elevation products near completion for the conterminous United States and Alaska respectively, NED data will soon be derived from these sources at a minimum. For the small areas that are not yet covered, the lower-resolution 30-minute and 1-degree USGS DEM products were interpolated to obtain values used in NED.