The National Map Seamless Server, Earth Resources Observation and Science (EROS)
Description The National Elevation Dataset (NED) 1 Arc Second is a raster product assembled
by the U.S. Geological Survey (USGS). NED is designed to provide National
elevation data in a seamless form with a consistent datum, elevation unit,
and projection. Data corrections are made in the NED assembly process to minimize,
but not eliminate, 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. As higher-resolution or higher-quality data become available, the NED 1 Arc Second 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. Specifications
Back To Top Format Information ArcGrid is an Arc/Info proprietary format. Some other software packages can read the ArcGrid format. Customers who specify ArcGrid will be delivered a workspace. The workspace is not tarred or gzipped. BIL is a non-proprietary format made by running the GRIDIMAGE command in Arc. The data is a simple binary raster format (signed integer data). There is an accompanying ASCII header file that provides file size information (number of rows and columns). The data are stored in row major order (all the data for row 1, followed by all the data for row 2, etc.). GridFloat is a non-proprietary format made by running the GRIDFLOAT command in Arc. The 32-bit (4 byte) is a simple binary raster format (floating point data). There is an accompanying ASCII header file that provides file size information (number of rows and columns). The data are stored in row major order (all the data for row 1, followed by all the data for row 2, etc.). More information about binary floating point is at:
TIFF for NED 1 Arc Second is a 32 bit floating point grid format. More information on the 32 bit floating point TIFF is at: Download Information
NOTE: Contact a Customer Service Representative (webmapping@usgs.gov) for custom product media options. * Bil is a binary integer point format ** TIFF is a 32 bit floating point grid format *** GridFloat is a binary floating point format | ||||||||||||||||||||||||||||||
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://seamless.usgs.gov/products/1arc.php
Page Contact Information: webmapping@usgs.gov
Page Last Modified: August 19, 2008
