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USGS National Elevation Dataset (NED) Coverage: Complete Coverage of Contintental US, AK, and HI Size: 40 GB (Compressed) 56GB Uncompressed Format: ArcGrid The data is grouped in 2 degree latitude by 6 degree longitude blocks. The blocks are named in the following format xxxyy, where xxx is the longitude (may only be 2 characters) and yy is the latitude (always 2 characters). Click Here for the Block Coverage Graphic (Continental US Only) Product Description: The 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 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. |
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