Here are the procedures for importing a GTOPO DEM (see link under Resources on HerpNET website) into ArcView:

Requirements: GTOPO DEM from USGS, Winzip, ArcView and Spatial Analyst Extension (an ESRI product which processes raster data)

  1. After downloading the zipped file, open without decompressing the tar file (this is an option in Winzip). Extract to a directory, where Winzip can place the handful of files.
  2. Rename the *.dem to *.bil
  3. Open ArcView, (make sure S.A. extension is checked on).
  4. Add theme as Image Data Source ; choose *.bil
  5. Highlight the newly added theme, in the drop down Theme menu, choose Convert to Grid
  6. In the dropdown Analysis menu, choose Map Calculator and apply the following formula: ([newgrid] >= 32768.AsGrid).con ([newgrid] -65536.AsGrid, [newgrid]) Obviously [newgrid] can be any name you choose.
  7. in dropdown Theme menu, choose Save Data Set, Save Map Calculator Theme (at the moment it is a temporary grid that "disappears" upon closing Arcview)
  8. Under the dropdown Surface menu, contours or hillshades files can be made.

Further tools for processing grids (like merging, clipping, smoothing grids to the extent that you want) can be found in a FREE extension called GridPig from ESRI written by a user (instructions included in download):

Any ArcView type questions can be posted to the HerpNET listserv too, since there's a growing body of users now. And I'm always happy to try to help. MK

-- Michelle S. Koo Biogeographic Systems Manager California Academy of Sciences Department of Herpetology Golden Gate Park, San Francisco, CA 94118-4599. USA