| # GRASS Help System

## DISTRIBUTION OF DEM DATA

The U.S. Geological Survey (USGS) produces and distributes 1-degree and 7.5-minute Digital Elevation Models (DEM). 1-degree DEM has a resolution of 100 meters, while 7.5-minute DEM has a resolution of 30 meters. Full 1-degree coverage is available for the United States. Although the USGS will eventually have full 7.5-minute DEM coverage for the U.S., only about 30&percent; coverage now exists. An index listing available 7.5-minute DEMs is published semi-annually and can be requested from the USGS. See "National Mapping Program, Technical Instructions: Data Users Guide 5" -- Digital Elevation Models.

When DEM data is not available for an area, there are two methods by which the USGS project can be expedited. The first is by prepayment of the standard purchase price ($100.00). Prepaid projects are worked ahead of most other projects. Although there is no guaranteed completion date, the data will be available sooner than it would otherwise be.

The second method involves sharing USGS production costs. Under this type of arrangement two parties split the estimated production costs. Cost sharing projects cost $500.00 per quad and are worked on before prepaid projects. They have an average production time of about 14 months. Though the production time is very long, the price is very reasonable. Without use of cost sharing needed quads might not be completed for years.

The USGS has a comprehensive distribution program for the 7.5-minute and 1-degree DEMs, along with other digital data and map products. Questions regarding availability and ordering of any USGS digital cartographic and geographic data should be addressed to:

National Cartographic Information Center (703) 860-6045
U.S. Geological Survey
507 National Center
Reston, Virginia 22092

Private companies can also produce digital terrain models. Two such firms, among many available, are listed below:

Markhurd Corporation POC: Joe Kiesow
345 Pennsylvania Ave. S. (612) 545-2583
Minneapolis, Minnesota 55426

SPOT Image Corporation (703) 620-2200
1897 Preston White Drive
Reston, Virginia 22091-4368

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Automatically created on: Sat Jan 8 06:50:25 2005