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This error is from data bases of 1:100,000 to 1:150,000 scale photography 
with base/height ratios from 1.0 to 0.6. The APPS error is the instrumental 
contribution of error from the 25yw.m least reading of the Datagrid. The 
correlation error is the human error in identifying points from the stimulus 
image to the data base. As described earlier, the correlation function is 
strictly a manual process whereby the operator selects the location of points 
on the data base. While operator experience and acuity have an effect, the 
7.3 meter is representative. 
There are several conclusions to be drawn from this analysis. 
a. The data base error is largely a function of photographic scale 
and resolution. That is, for larger scale and better resolution of 
equivalent cartographic quality, the error would be reduced. 
b. Increasing the instrumental accuracy of the APPS will have a 
minimal effect on the total accuracy for data bases of a scale of 1:100,000 
or smaller. For example, for data bases of this quality, reducing the 
APPS error to zero will only decrease the total error by 1 meter. This 
suggests that greater complexity or precision for the mensuration would 
not be cost effective. 
c. The correlation error is a function of the quality and scale of the 
stimulus imagery. The best results were obtained with stimulus images from 
frame photography at a scale of 1:10,000.