How To: Convert GTOPO30 DEM data to a grid using ArcGIS

Summary

You can use ArcGIS Spatial Analyst to convert a United States Geological Survey (USGS) GTOPO30 digital elevation model (DEM) to an ESRI grid format.

Click the USGS GTOPO30 link in the Related Information section to download a GTOPO30 DEM. This file comes as a .tar file, which contains the *.dem and *.hdr files. Both files are required for this operation.

Procedure



  1. Uncompress the TAR file using WinZip 6.2 or higher.
    <a href='http://support.esri.com/en/knowledgebase/techarticles/detail/17135' target='_blank'>How To: Fix WinZip configuration and avoid data corruption</a>

    Warning:
    If not properly configured WinZip can corrupt the files.

  2. Change the *.dem extension to *.bil.
  3. Open ArcCatalog.
  4. Navigate to the *.bil created in Step 2.
  5. Right-click on the *.bil, click Export, and click the Raster to Different Format option. Specify the location to which you will save the new grid, and ensure the Save As Type is set to ESRI GRID.
  6. Open ArcMap and add the grid created in Step 5.
  7. On the ArcGIS Spatial Analyst toolbar, click Spatial Analyst and select Options.
  8. Click the General tab and set the working directory.
  9. Click the Extent tab and set the analysis extents to Same as layer 'your grid'.
  10. Click the Cell Size tab and set the cell size to Same as layer 'your grid'. Click OK.
  11. Navigate to ArcGIS Spatial Analyst and select the Raster Calculator. Enter the following expression, substituting your grid for [in_grid]. Include the square brackets.

    Code:
    CON([in_grid] >= 32768,[in_grid] - 65536,[in_grid])

    Click Evaluate.
  12. The ocean areas (-9999) can be converted to NODATA using the SETNULL function. Insert the Calculation from Step 11 for [Calculation]. Include the square brackets.

    Code:
    setnull([Calculation ] == -9999, [Calculation ])

    Click Evaluate.
  13. Save the final output to disk by right-clicking the Calculation result from Step 12 and selecting Make Permanent.

Related Information