UNFRAG - large tracts of unfragmented lands based on USGS
National Land Cover Data Set, Version 05-25-99.  

Generalized USGS Land Cover classes:

                      10's = water
                      20's = urban
                      30's = barren
                      40's = forested
                      50's = shrubland
                      60's = orchards
                      70's = grasslands
                      80's = planted/cultivated
                      90's = wetlands

All classes except 20 (urban) were considered "natural
communities".   Nongravel roads from the NH DOT road centerline 
data were used to create the unfragmented blocks.

Fields in the UNFRAG data set include:

1.  GRID-CODE:   1 = Unfragmented natural community, with
                     acres >= 500.  But as noted in the Process.txt
                     file, there are some features coded as 1
                     that are artifacts of the data structure,
                     and don't really reflect this definition.
                     It is recommended that users rely on 
                     the UNFRAG field for querying/selecting.
                     (It is left in this version only so that the
                     process steps may be followed.)
                 9 = Other features

2.  UNFRAGACRES  Acreage of each polygon

3.  UNFRAG       1 = Unfragmented natural community of >= 500 acres
                 0 = Other

4.  UNFRAGCLASS  Acreage class for unfragmented communities, where
                 UNFRAG = 1 and   500 <= ACRES <  1000
                          2      1000             1500
                          3      1500             2500
                          4      2500             5000
                          5      5000            10000
                          6     10000