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over the map extent. This work provided a starting point for this study. The fuzzy set analysis
described earlier was used in conjunction with kriging to produce a fuzzy spatial view of accuracy.
14.2 BACKGROUND
A LC map, or map of the natural vegetation communities, water, and human alterations that
represent the landscape (e.g., agriculture, urban, etc.), provides basic information for a multitude
of applications by federal, state, tribal, and local agencies. Several public (i.e., the USDA Forest
Service and USDI Fish & Wildlife Service) and private (i.e., The Nature Conservancy) agencies
use meso-scale LC maps for local and regional conservation planning. LC maps can be used in
land-use planning, fire modeling, inventory, and other applications. Because of their potential for
utilization in a variety of applications by different users, it is important to determine the thematic
map accuracies.
A thematic accuracy assessment was conducted on the northern half of a preliminary Arizona
Gap Analysis Program (AZ-GAP) LC map (Graham, 1995). The map (Plate 14.1) was derived
primarily from Landsat Thematic Mapper (TM) satellite imagery from 1990. Aerial video and
ground measurements were used to facilitate classification of spectral classes into 105 discrete
cover types for Arizona using a modification of the classification system by Brown et al. (1979).
This system attempted to model natural hierarchies in the southwestern U.S. However, Graham's
procedures were not well described or documented.
The preliminary LC map consists of polygons labeled with cover types contained in a GIS with
a 40-ha minimum mapping unit (MMU); MMUs were smaller in riparian locations. This resolution
is best suited for interpretation at the 1:100,000 scale (meso-scale).
14.3 METHODOLOGY
14.3.1
Reference Data
A random sampling design, stratified according to cover type, was used to determine the set of
polygons to be sampled in the accuracy assessment. A total of 930 sampling sites representing 59
different cover types in northern Arizona were visited during the summer of 1997. Field technicians
identified dominant, codominant, and associate plant species and ancillary data for a 1-ha area. The
field data at each site were assigned to one of the 105 cover classes by the project plant ecologist
using the incomplete definitions provided by Graham. Each reference site was tied to the GPS-
measured point location at the center of the 1-ha field plots. The resulting reference data set,
therefore, consisted of 930 points with a field assigned cover type and associated point location.
14.3.2
Binary Analysis
Traditional measures of map accuracy were calculated by comparing the cover label at each
reference site to the map. Matches between the two were coded as either agreed (1) or disagreed
(0). These statistics were incorporated into an error matrix from which user's and producer's
accuracies for each cover type were calculated, as well as overall accuracy of the LC map.
14.3.3
Fuzzy Set Analysis
The Gopal-Woodcock (1994) fuzzy set ranking system was refined for application to the
reference data for the northern AZ-GAP LC map (Table 14.1). The fuzzy set ranks reflected a
hierarchical approach to LC classification. While Gopal and Woodcock (1994) suggested that fuzzy
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