1. Apparent Differences (A) 
a. Both decisions possible 
b. Changes in land use 
c. Boundary differences 
2. Real Differences (B) 
a. Differences within groups of open space (unit and 
sub unit level) where B4W was assessed as correct 
decision and CIR as an error. 
b. Differences within groups of open space (unit and 
sub unit level) where CIR was assessed as correct 
decision and B4W as an error. 
c. Differences between groups of open space (group and 
unit level) where B+W was assessed as correct and 
CIR as an error. 
d. Differences between groups of open space (group and 
unit level) where CIR was assessed as correct and 
B+W as an error. 
e. Not clear situation in both photographs: decision 
not possible and field check is necessary. 
Analysis of Differences (Figure 11) 
l. Apparent Differences (A) 
a. Both decisions possible 
This occurred when the cross landed on a certain land use 
type on the one photograph whilst the identical cross did not 
land on the same point on the other photograph - due to orientation 
difference, slight scale difference, etc. In that case the 
decision was made using the information on the print and by 
mobilizing the "mental square image". (See Figure 4). 
If, for the same cross, for the B4W photography the decision 
was A and for the CIR the decision was B, the land use pattern 
inside the mental square image suggests the possibility of both 
the decisions being correct. A number of 176 such cases were 
recorded for the three enumeration districts. 
b. Changes in land use 
Disagreements due to land use changes were recorded. The 
B+W aerial photography was 1974 cover and the CIR was 1975 
cover: both taken in summer. Such changes in land use are 
likely to occur in a period of one year. A number of 8 such 
cases were recorded, 
      
   
   
    
    
     
    
    
  
   
   
    
    
   
    
   
    
   
   
      
>+A 53000 AQ