The layer we are running with is an amalgam of three federal agency GIS products, ALRIS, and some internal info:
 
A) Southwest ReGAP: USGS interpretation of satellite imagery acquired 1998-2002.
B) BLM interpretation of aerial photography (DOQQs) acquired 1992-1997 .
C) USGS records for irrigated lands current through 2001.
Medium to High Density Urban and Industrial = Derived from "A" above.  Impermeable surface 50% to 100%.  Includes mines.
 
Rural / Low to Mixed Density Development = Derived from "A" and "B" above.  Impermeable surface is 10 to 49%.  Agricultural activity may be present.  Native vegetation may be present.  
 
Agriculture Only = Derived from "A" and "C" above.  Crops account for 20% or more of total vegetation.  Impermeable surface is less than 10%.
 
Protected or Federal Mulitple Use = ALRIS plus some of our internal data on conservation properties and easements.  This doesn't include all the recent Pima County bond lands


Mike List, TNC, 5/2/06