LAKE ONTARIO 
use of aerial imagery and go to another data source. 
If a surrogate is present go to 2. 
2. Devise a stepwise elimination procedure to isolate the various 
features of interest using image surrogates as substitutes 
for the features of interest. Continue. 
3. Using an air photo interpreter, test the procedure against 
ground data. If the results are satisfactory go to 4. If 
the results are not satisfactory go to 1 and evaluate each 
step. 
4. Using information from 3 train staff to carry out the proce 
dure . 
In the work described here it was found that step la 
necessitated the creation of a model of the farm in order to 
better assess the most meaningful of the spatial surrogates avail 
able. A corollary is that the scientist who seeks to develop 
this approach for application to his own problem is often forced 
to adopt a unique perspective of his subject matter. This per 
spective may well yield unforseen benefits. 
FARM MODEL 
The system under study here is the livestock crop economy 
of southern Ontario, Canada. Of specific interest is the indivi 
dual farm in central southern Ontario. (See Fig. 1). 
FIGURE I SooMtom Ontario Toot «Ita* 
ORONTO