About the USGS data formats: You can get "Data Users Guides" from the
USGS on their various data formats, such as the 1:2000000,1:100000, or
1:24000 dlgs, DEMs, Land Use and Land Cover Digital Data...
Call 1-800-maps or 1-703-860-6045 or write to
Earth Sciences Information Center
USGeological Survey
507 National Center
Reston, VA 22092
-N.