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Product Description

The National Elevation Dataset (NED) is a seamless raster product derived primarily from USGS 30-meter Digital Elevation Models (DEMs), along with higher resolution data where available.

NED data for the conterminous United States, Hawaii, Puerto Rico, the Pacific Islands, and the Samoan Islands is expressed in geographic coordinates (latitude/longitude). It is horizontally referenced to the North American Datum of 1983 (NAD83) and vertically referenced to the North American Vertical Datum of 1988 (NAVD88). The resolution is one arc-second (approximately 30 meters). NED data is also available at 1/3 arc-second resolution (approximately 10 meters) for some areas of the conterminous United States.

NED data for Alaska is expressed in geographic coordinates (latitude/longitude). It is horizontally referenced to the North American Datum of 1927 (NAD27) and vertically referenced to the North American Vertical Datum of 1929 (NAVD29). The resolution is two arc-seconds (approximately 60 meters).

The following products are available:

• NED Seamless

The product consists of seamless raster data which is provided according to a user-specified area of coverage. Instantaneous download is available for areas up to 30 square degrees latitude/longitude (in 100 mb files).

The data is available in four formats:

1. ArcGrid is a proprietary format, which is primarily used in ArcInfo. However, some other software packages can also read this format. The ArcGrid format is delivered as a workspace, which is not tarred or gzipped.

2. GRIDFLOAT is a non-proprietary format created by running the GRIDFLOAT command in Arc. It is essentially a floating-point binary data file with accompanying ASCII descriptor files.

3. BIL is a non-proprietary format created by running the GRIDIMAGE command in Arc. The BIL format will be more compact that the ArcGrid format. It consists of an integer binary file with accompanying ASCII descriptor files. The BIL integer format is recommended for software packages that do not support floating-point data.

4. TIFF is a 32-bit floating point grid format.



• NED 30m Pre-Defined Areas

The 30m Pre-Defined Areas consists of NED data for the conterminous United States, Alaska, Hawaii, Puerto Rico, the Pacific Islands,and the Samoan Islands. The majority of the conterminous US files are provided in blocks of 2 degrees latitude by 6 degrees longitude. Alaska files are provided in blocks of 1 degree latitude by 1 degree longitude. Files for Hawaii, Puerto Rico, the Pacific Islands and the Samoan Islands are provided in blocks of variable geographic areas. The full dataset consists of 110 pre-defined CDs.

The NED 30m Pre-Defined Areas are updated every 2 months with the best available elevation data.

NED 30m Pre-Defined Areas are available in two formats:

1. ArcGrid is a proprietary format, which is primarily used in ArcInfo. However, some other software packages can also read this format. The ArcGrid format is delivered as a workspace, which is not tarred or gzipped.

2. GRIDFLOAT is a non-proprietary format created by running the GRIDFLOAT command in Arc. It is essentially a floating-point binary data file with accompanying ASCII descriptor files.

Additional Information:

NED Homepage
NED Fact Sheet (Download Adobe Acrobat Reader)
GISDATA Web Mapping Portal
NED Data Dictionary
NED Release Notes

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U.S. Department of the Interior | U.S. Geological Survey
URL: http://eros.usgs.gov/
Page Contact Information: custserv@usgs.gov
Page Last Modified: August 22, 2006