The following is an excerpt from a paper submitted by RECON Enviromental,
Inc. Titled "Land Cover Data Assessment in Pima County"


EROS

In 1993, multiple federal agencies, including USGS, Environmental
Protection Agency  (EPA), National Oceanic and Atmospheric
Administration (NOAA), and U.S. Forest Service (USFS) combined
resources to purchase Landsat Thematic Mapper satellite imagery
covering the entire United States. USGS/EROS Data Center took the
lead to process the data and develop a national land cover
database. The Pima County EROS coverage is part of that database.
 
The EROS land cover map is based on classification of 30-meter
resolution imagery from 1992. For the national database,
scientists used a variety of supporting information in addition
to the satellite data, including topography, census, agricultural
statistics, soil characteristics, other land cover maps, and
wetlands data to determine and label the land cover type for each
30-meter pixel (USGS 2000; EPA 2000). Twenty-one classes of
land cover are mapped, using consistent procedures for the entire
U.S. Because land cover classes are generic enough to be applicable
nationwide, vegetation is broadly differentiated based on structure
(i.e., grassland, shrubland, forest). Non-natural vegetation and
non-vegetation classes are more finely differentiated with multiple
classes for urban and agricultural land cover types.  High
resolution mapping of urban and agricultural land cover make this
data set potentially useful for Pima County. Pima County DOT used
the EROS data to update GAP's generic "urban" polygon for Green
Valley. This gives a better picture of land cover for this area,
which is a mosaic of commercial and industrial development, various
types of agriculture, and natural vegetation. This data was not
incorporated into the composite land cover map at this time since
its accuracy is uncertain, its land cover classification does not
fit the needs of the SDCP, and its high resolution is not appropriate
for county-wide analyses.  Procedures to evaluate the accuracy of the
national land cover database have been developed, and private
contractors are completing accuracy assessments for each state.
Metadata and accuracy assessments are currently unavailable for
Arizona. A comparison of the EROS data and the WHIP urban/suburban
land cover classes would be informative if the WHIP data become
available. Prior to using the EROS data, land cover types should be
cross-walked into a modified land cover classification for the SDCP.
Also, 30-meter pixels should be aggregated to better describe urban,
suburban, and agricultural patterns on the landscape at the scale of
SDCP analysis.