Import DEM / CDED

USGS DEM files contain elevations in a regular grid, derived from USGS topographic map contours or directly from aerial photography.

The CDED consists of an ordered array of ground elevations at regularly spaced intervals. It is based on National Topographic System (NTS) maps at the 1:250,000 scale. Nearly complete coverage of Canada is available. CDED data use the same physical format as USGS DEM data, and therefore can be displayed by Global Mapper.

Load these files directly with the following recognized extensions: *.dem; *.dem.gz; *.dat; *.gz; *.1; *.2

Import support is also available for CTM DEM (*.dem), ENVI DEM (*.dat; *.envi; *.hdr), GTOPO30 (gt30*.dem) DHM Swiss DEM (*mbl, *.mlt), GSD Swedish DEM (*.gsd), Helava DEM (*.dte), Japanese DEM (*.mem; *.lem; *.mem.gz; *.lem.gz), MicroDEM DEM (*.dem), Swedish DEM (*.dat), and other related DEM formats.

Export DEM / CDED

The Export DEM command allows the user to export any loaded elevation grid data sets to a native format USGS DEM file.

Export DEM or CDED files from the File> Export menu by choosing Export Elevation Grid Format... or Export Raster/ Image Format.... and specifying DEM or USGS DEM as the Export Format. Individual layers can also be exported from the Control Center by right-click on the layer and going to Layer > EXPORT. Multiple files can be batch converted to and from the format from the Batch Convert/Reproject tool.

When selected, the command displays the DEM Export Options dialog which allows the user to setup the export. The dialog consists of a General options panel which allows the user to set up the quadrangle name, grid spacing and vertical units.

Note: Global Mapper will export a DEM or CDED file in any supported projection. To generate a USGS compliant DEM, make sure the display projection is set to the appropriate geographic, UTM or State Plane projection and datum.

Quadrangle Name

A descriptive name identifying the map. This is typically named by a local physical feature.

Vertical Units

Select from the following options:

  • Meters
  • Decimeters
  • Centimeters
  • Millimeters
  • Feet
  • Decifeet
  • Inches
  • Centifeet
  • Millifeet

Note: DEM files store elevation values as integers. To maintain precision in the output file, specify a small vertical unit, such as Centifeet, Millimeters, etc.

Format Updates

19.1 Improved support for import and export of USGS DEM with International Feet as the units for a State Plane projection.[Item #20175]
16.0 Added a Graph and Chart Manager under the Analysis menu to allow creating graphs and charts from loaded data., including histograms for gridded terrain layers (i.e. DEMs)
12.2 Added support for ENVI DEM files with 32-bit integer samples.
8.3 Make default export elevation units for DEM and Global Mapper Grid exports be decimeters if metric units are the default so that the full precision of nearly all data sets will be preserved by default.
7.4 Added support for loading Japanese DEM (JDEM) .mem files.
7.3 Made the filling in of small gaps work when exporting DEM files with arc degrees as the current view/export units on the Projection tab of the Configuration dialog.
7.2 Added option to write an invalid datum code to DEM files when exporting with a view/export datum set to one that is not supported by the DEM format.
7.0 Manually compute the min/max sample values for USGS DEMs that have a non-unity Z resolution since they are often stored incorrectly, resulting in odd shading in Global Mapper. This will apply to things like decimeter and centimeter DEMs.