ory. 
'ding 
vw. 
N 
AT 
tify 
ak 
on 
otos 
within the map sheet, the number of strata occuring within the 
Category 
- Average slope less than 10$ 
- Average slope 10$ - 40$ 
- Average slope over 40$ 
Level VI: DEGREE OF STOCKING 
The following tree density classes were recognized on the 
aerial photographs: 
Category 
1. High - areas having tree density more than 60$ 
2. Medium - areas having tree density 40$ to 602 
3. Low - areas having tree densitv up to 40% 
5.3. Time and work study 
There were 938 aerial photographs to be interpreted covering 14 
full topo-sheets of scale 1:63,360 (15' x 15') and 14 part topo- 
sheets of the same scale. According to the work studv carried 
out some 450 working davs were needed to complete the actual 
photo-interpretation work. Since there were three trained photo- 
interpreters, the work was completed in five months period. Ac- 
cording to the experience gained it took some 10 working davs 
to complete the PI work of one mapsheet which consisted of about 
10 stereo models. 
5.4. Field checking 
Before transfering the PI details on to the map, a field checking 
was organised. The interpreted ohotographs were selected on ran- 
dom basis and taken to the field for checking the details. About 
fifteen days were spent in the field, wherein all the photo- 
interpreters carried-out the checking work. The aerial photo- 
graphs interpreted by a photo-interpreter were exchanged with 
each other for field checking purposes. This was done with the 
view of avoiding bias and ensuring improved accuracy. 
6. Transfer of PI details on to the topoman 
The situation of availability of base maps within the project 
was not very satisfactory. Topo sheets were available on vary- 
ing scale, namely 1:25,000, 1:50,000 and 1:63,360. For catch- 
ment III (see map 2) the base maps on an uniform scale of 
1:25,000 were available whereas for catchment I & II the base 
maps existed on varying scale mentioned above. 
The work of transfer of PI details from aerial photographs was 
carried out with the help of sketchmaster and also ocularly. 
Help of Survey of India Organization was sought. firstly to get 
the work done through trained and experienced draftspersons and 
secondly to complete the target within the short period at 
disposal. 
The number of days required to transfer the PI details from 
aerial photographs on to the 1:63,360 scale (1" = 1 mile) map- 
sheet depend mainly on two factors: the forest area occuring