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3.5: What is DEM? (Geographic Information Systems)




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This article is from the Geographic Information Systems FAQ, by Lisa Nyman lnyman@census.gov with numerous contributions by others.

3.5: What is DEM? (Geographic Information Systems)

From: David Mark (dmark@sun.acsu.buffalo.edu)

The terminology in this area is somewhat complicated. The U.S.
Geological Survey does indeed have a 'product' that is called "Digital
Elevation Model". These are gridded elevation data, 30 m resolution.
Standard data sets cover 7.5 minute by 7.5 minute areas equivalent to
USGS 1:24,000 scale maps. The USGS has another data-set series called
"Digital Terrain Models", most or all of which were originally
developed by the US Army and/or Defense Mapping agency, from 1:250,000
scale maps.

Outside of USGS, there is some disagrement in the literature as to
whether "Digital Elevation Model" (DEM) is a _generic_ term for all
digital data for elevations, including TINs, digitized contours, etc.,
or whether the DEM term should be restricted to regular rectangular
grids. Those who prefer to restrict the term DEM to grids often prefer
to use "Digital Terrain Model" (DTM) as the _generic_ term for all
computerized elevation data.

Bruce Gittings maintains a Digital Elevation Data catalogue, which is posted
monthly on GIS-L. This catalogue, which is regularly updated, contains
descriptions of a large number of topographic and bathymetric datasets with
local, regional and global extent. There are also useful references to a
number of other types of data (eg. USGS products, Digital Chart of the World,
regional databases for Asia, Europe etc.). It is well worth checking this list
before looking elsewhere for data.

The most up-to-date version of this catalogue is available through the
Edinburgh GIS WWW server.

WWW URL:
http://www.geo.ed.ac.uk/home/ded.html

The catalogue is also available through a mail server. Send e-mail to
geoinfo@geovax.edinburgh.ac.uk for full details of how to use this service.

DEMs are available from spectrum.xerox.com [192.70.225.78], /pub/map

Contact:
Lee Moore -- Webster Research Center, Xerox Corp.
Voice: +1 (716) 422 2496
Arpa, Internet: Moore.Wbst128@Xerox.Com

For information on converting DEM to ARCVIEW format, see
http://www7440.nrlssc.navy.mil/muse.html

 

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