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    Data  Format

    All layers are ARC/Info coverages and grids, which have been exported and gzipped on a UNIX machine.  After downloading, each file must be unzipped and imported into ARC/Info or Arcview.

    All coverages and grids: (except the California county boundaries coverage)

       
      Projection:  UTM zone 10
      Horizontal datum:  NAD83
      Spheroid:  GRS1980.


    This is compatible with GPS data collected in UTM using the NAD83 datum, given the resolution of these datasets. (GRS1980 is not exactly the same as WGS84, but at this resolution, they are virtually identical.)

    Some of the grids and coverages had to be reprojected to match the others.  The NADCON datum transformation in ARC/Info was used for all conversions.  Read the metadata files for details about individual datasets.