Figure l.vStudy site (1) In Northeastern Brazil, principally in 
Paraiba but partly in Rio Grande do Norte. The location of 
the northeastern area is shown on the inset map of Brazil. 
Geometric Correction and Map Production 
Geometric correction was applied only after all operations were 
performed. Eleven control points of high degree of analyst confidence on 
both the SPOT false-color composite and the corresponding topographic map 
received from SUDENE (1972) at the scale of 1:100,000 were selected. The 
X and Y coordinates from the image were recorded for each of the 11 
points. The image positions of these coordinates were interactively 
identified and an affine transformation matrix was calculated (RMSE <1 
pixel). None of the control points was rejected. The final matrix based 
on all 11 control points was applied to both the SPOT image data and 
thematic maps to perform the transformations necessary to reference the 
data to the Universal Transverse Mercator coordinate system. The image 
data were resampled to 20 meters using a cubic convolution algorithm; 
whereas, thematic maps were resampled using a nearest neighbor 
algorithm. Finally, the seven types of earth resources information 
listed previously were derived from the geometrically corrected image. 
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