446 
for example, are those caused by incorrectly classifying an 
area as dieback when it is not and errors of omission are 
those areas of dieback in the field which were classified 
healthy in the interpretation. These are shown in Table 2. 
Table 1 
Comparison of Photo Interpretation Results 
with Ground Transects for Two Film Types 
Map Type 
70 mm 1 : 3,000 
230 mm 1 : 40,000 
Interpreted 
(metres) 
Field 
transect 
(metres) 
Interpreted 
(metres) 
Field 
transect 
(metres) 
Type A 
13,600 
A 13,300 
BC 300 
C 0 
14,850 
A 14,000 
BC 850 
C 0 
Type BC 
2,500 
A 400 
BC 2,100 
C 0 
1,440 
A 640 
BO 800 
G 0 
Type C 
280 
A 0 
BC 0 
C 280 
200 
A 0 
BG 0 
C 200 
Tabie 2 
Reliability of Interpretation 
(from Table 1) 
Type 
1:3,000 
1 : 40,000 
Reliability 
A 
VO 
00 
94*5 
BC 
84$ 
56*5 
0 
100*5 
100*5 
Errors of Commission 
A 
2$ 
6$ 
(as a $ of the 
BC 
16*2 
44*5 
interpreted type) 
c 
0*5 
0*5 
Errors of Omission 
A 
3 % 
4*5 
(as a $ of the 
BC 
12$ 
52*5 
field type) 
0 
0*5 
0*5