MacDEM - a DEM viewer, editor, and converter for the Mac






DEM Files



  User's Guide


DEM Files - Where to Get Them

Format Resolution Coverage
Seamless (below) 1 arcsec (~30 m)
1/3 arcsec (~10 m)
1-degree DEM (below) 3 arcsec (~100 m) U.S.
7.5-minute DEM (below) 30 m U.S.
DTED Level 0 (below) 30 arcsec (~1 km) Worldwide
GTOPO30 (USGS) 30 arcsec (~1 km) Worldwide
GLOBE (NOAA) 30 arcsec (~1 km) Worldwide
TerrainBase (NOAA)
(get .bin and .hdr file)
varies Worldwide

More sources are listed at the bottom of this page.

Seamless DEMs

USGS Seamless Data Distribution System has downloadable DEM files for the United States. The user interactively selects the desired coverage area and a DEM is constructed for that area (hence, "seamless"). Data are available from the National Elevation Dataset (NED), which is the "best available" DEM data. Shuttle Radar Topography Mission (SRTM) data are also available.

Make sure to select BIL or GridFloat format before downloading (they are not the default). Do this by clicking the "Modify Data Request" button before downloading. In the window that pops up, select BIL or GridFloat from the pop-up menu in the Data Format column. Then scroll to the bottom and click on "Save Changes and Return to Summary." (Other formats are available, but MacDEM only handles these two. The others are proprietary formats.)

The SDDS web site is picky about what browser you use. One person reports success using Netscape 7. I've been able to use IE 5 to select the coverage area, but the downloads fail, so I copy the URL from the download page into Netscape 4.75 to do the actual download.

1-degree and 7.5-minute DEMs

USGS US GeoData has downloadable ASCII- and SDTS-format DEM files for the United States. Note that 1-degree DEMs are also called 1:250,000 DEMs, and 7.5-minute DEMs are also called 1:24,000 DEMs. I believe these scales refer to the scales of paper maps that cover the same areas, since the data in electronic form has no intrinsic scale.

If you know a latitude and longitude you can find the 1-degree DEM that covers it using the 1-Degree DEM file finder


  • Since uncompressed ASCII DEM files are very large (e.g. nine megabytes for a 1-degree DEM), I recommend that they be downloaded in compressed (.gz) form and expanded using MacGzip.
  • SDTS files are downloaded as gzip'd TAR files. Use MacGzip to uncompress the .gz file. Place the resulting .tar file in a folder by itself and use suntar to extract the individual files. If the browser and MacGzip are set to create files with the proper type and creator codes, unpacking a downloaded SDTS file is as simple as placing the .gz file in a folder by itself, double clicking it, then double clicking the resulting .tar file. Some people use Stuffit Expander instead.
  • IMPORTANT! Make sure MacGzip is in binary mode when uncompressing SDTS files! Otherwise the data can be corrupted. In MacGzip go to Preferences under the Edit menu. In the dialog box that appears, select "decompression" from the pop-up menu. In the other pop-up menu that appears, select "Binary (Raw)" instead of "ASCII".
  • Older SDTS files have an error in the geopositioning data. MacDEM attempts to correct for this error.


DTED Level 0

NIMA Geospatial Engine has a map-based interface for accessing DTED Level 0 and image downloads. I was able to download DTED data using Mac OS 8.1 + Netscape 4.5.

(Earth-Info is another map-based interface, but it just links to the Geospatial Engine to get data. Plus, it says it needs MacOS9+IE5+MRJ2.1 or Windows+IE5 or NS4.5.)

GIS Data Depot also has DTED Level 0 worldwide and for the United States. However, elevations below sea level are corrupted.

DTED Level 1 (3 arcsec, ~100m) and Level 2 (1 arcsec, ~30m) data are not publicly available.
Samples of DTED level 1 and level 2


Other DEM Sources

California State University Northridge, Department of Geography has 7.5-minute DEM files for the western United States. For example, the state of California is accessible by name or by map, with an underlying directory structure grouped by degree. Files ending with ".CDO" appear to be MacBinary files. Use MacBinary or Stuffit Expander to convert them to usable form.

Geography Department of the University of Hawai`i at Manoa has DEM data for Hawaii including 1:24,000 data (look for elev.dem files)

University of California, Berkeley has San Francisco Bay area DEMs, and links to other California DEMs. Also has 10 meter DEMs

Estuarine Bathymetry Home Page (NOAA-NOS)

Sea Floor Topography - go to "ftp digital gridded data", then download topo_8.2.img

Pennsylvania State University Earth System Science Center Database
  North America/US48 DEM models has 500m DEMs
  Worldwide DEM models includes ETOPO-5

USGS Tahoe area 30m and 10m DEMs

Idaho Geospatial Data FTP (includes DEM)

Shuttle Radar Topography Mission (SRTM) Main page
  Download page

Utah 10m DEMs PC .exe self-extracting archives
  FTP site

University of Washingtion Geospatial Archive
  7.5 Minute (10 Meter) DEMs (Washington State)

Washington and Oregon State 10 m DEMs at the Regional Ecosystem Office

Yukon 90m DEMs at Yukon Renewable Resources

Created: 1998.10.24
Updated: 2006.09.25