HOWTO import USGS elevation data

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Revision as of 17:51, 26 September 2007 by Hajhouse (talk | contribs) (1/3 arc second = about 10 meters)
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The US Geological Survey offers a variety of digital elevation models through the Seamless Distribution System. The highest resolution offered is 1/3 second (= about 10 meters) with coverage of much of the USA. Here is an approach to working with them in GRASS.

Importing USGS 1/3 arc second NED datasets into GRASS

1. Download the datasets you desire through the provided web interface. They will arrive in a zip archive of a directory containing a subdirectory containing a file called w001001.adf, which is the main data file (tip: this is the biggest file).

2. Create a new GRASS location to work with the DEMs.
Pick one DEM to start with. From a GRASS shell:

cd 18437824/18437824 (example directory names --- replace with your actual names) location=name_of_your_new_location in=w001001.adf out=dem

3. Start GRASS (or restart) in the new location.

grass name_of_your_new_location/PERMANENT

4. If you have more than one DEM archive, import additional files as needed (note the -e flag, which causes the location's bounds to be extended to accomodate the new data): -e in=w001001.adf out=dem2
.. etc.

5. Use r.patch to combine the tiles into one continuous map, if desired.

Alternatives to the USGS DEM data

Other sources of digital elevation models include:

  • SRTM 90 data in TIFF format from These come in 5 degree by 5 degree tiles. Horizontal resolution: 3 arc second (90 m at equator). Coverage: world.