132 
In the primary research, from which this paper is derived, 
income is expressed as the production value per acre (or amount 
the farmer could afford to pay per acre for land, based upon 
its production). The value is obtained through the capitaliza 
tion formula: 
Return per acre 
7% 
x 100 
Production Value 
Where: 7% represents the interest rate prevailing for the 
farmer's land mortgage. 
A very troubling assumption to many who have reviewed 
this work is the modeling of individual farm productivity by 
using average production values. This may account for some 
of the errors found, however it is assumed that the efficient 
farmer will not just have high yields, but will also have 
more acreage in high return crops as compared to the poorer 
farmer. It should also be noted that usually the difference 
in output between two crops (for example hay and corn) is 
much greater than the difference within a given crop. 
With this very simplistic outline of what is a rather 
complex system one may use the aerial photograph and apply 
the new methods suggested here. 
APPLICATION OF THE METHOD 
The method used to interpret the photographic image 
requires one to be able to differentiate agricultural crops on 
1:15840 mid-summer imagery and to be able to determine the type 
of farm. All further contacts with the image require measure 
ments only. 
Experiments at the University of Waterloo showed that 
117 of 120 geography students who were studying their first 
course in aerial photographic interpretation, could interpret 
crops with an accuracy of 82 to 100 per cent. The top one- 
quarter of the class achieved an average accuracy of 95 per 
cent. 
Farm type may be identified by using the Crop Triangle 
developed in earlier work (Ryerson & Wood 1971) (and computer 
ized for this work) and careful analysis of buildings. 
Table II provides an indication of the method's built 
in complexity. The interpreter then uses crop acreage and 
building size to determine the number of livestock and the 
total output of livestock and crop products for each farm. 
All further calculations were done using a high speed digital