| Abstract
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These data were removed from the State Library web site because better data are easily obtainable from the U.S. Geological Survey. Please read about the current data at http://ned.usgs.gov/about.html and use the Data link to obtain the data.These data are a series of files derived from the National Elevation Dataset that each cover 16 USGS 7.5-minute quadrangles, (a 30x30-minute area), plus the area around those quadrangles required to fill in a rectangle in the coordinate system of the file.There are four versions of the data:
The "data" folder contains data in USGS DEM format, in Montana State Plane coordinates, NAD83, units meters. The elevations in these files are rounded to the nearest meter. These files were made at a time when ESRI did not support this coordinate system for DEM format files, and modern software may be unable to read the spatial reference from these files.The "utmdata" folder contains data in USGS DEM format, in UTM zone 11, 12, and 13 coordinates, NAD83, units meters. The elevations in these files are rounded to the nearest meter.The "fdata" folder contains data in Esri GridAscii format, in Montana State Plane coordinates, NAD83, units meters. The elevations are rounded to the nearest 1/100 of a meter.The "utmfdata" folder contains data in Esri GridAscii format, in UTM zone 11, 12, and 13 coordinates, NAD83, units meters. The elevations are rounded to the nearest 1/100 of a meter.The National Elevation Dataset (NED) is a seamless mosaic of best-available elevation data. The 7.5-minute elevation data for the conterminous United States are the primary initial source data. In addition to the availability of complete 7.5-minute data, efficient processing methods were developed to filter production artifacts in the existing data, convert to the NAD83 datum, edge-match, and fill slivers of missing data at quadrangle seams. One of the effects of the NED processing steps is a much-improved base of elevation data for calculating slope and hydrologic derivatives.The NED for Montana as of 4/1/2002 was donated to the Montana State Library by the Bureau of Land Management Montana/Dakotas office in Billings. The State Library combined the 30- and 10-meter DEMs into a single statewide dataset at 30 meter resolution and extracted data from that dataset to create these data files.
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| Purpose
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Geospatial elevation data are utilized by the scientific and resource management communities for global change research, hydrologic modeling, resource monitoring, mapping, and visualization applications.
DEMs can be used for creation of slope maps, aspect maps, shaded relief maps, and contour maps; for analysis of hydrography and runoff; for analysis of solar radiation received on the land; for determination of what part of the landscape is visible from various locations; for estimation of volumes of proposed earthworks or reservoirs; and for analysis of difficulty of traversing the terrain.
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