WORKING GROUP 4 
FRANCIS 
207 
of horror up the backs of senior surveyors, is the relatively low standard of 
mapping accuracy which is acceptable to most foresters and indeed in most 
pre-investment surveys. Topographic maps at a scale of 1 : 25,000, in hilly 
country, with form lines at 20 metres vertical interval, are perfectly adequate 
for the purposes of pre-investment studies. Admittedly maps at a larger scale 
and with a closer vertical interval between the contours would be desirable, 
but the cost is out of all proportion to the additional information obtained. 
One of the features which makes aerial survey work so attractive to the 
forester is its low cost, and one of the greatest problems which I personally 
have found is to convince the photogrammetrist and the ground surveyor that 
form lining on the tree tops with an error of plus or minus five or ten metres 
is quite acceptable in dense tropical forest. This form lining on the tree tops 
has been adequately described elsewhere in photogrammetric papers, but it 
works remarkably well in practice, even over the densest tropical forests. 
Admittedly it is difficult to fix a definite datum, but modern photogrammetric 
machines mean that the vertical spacing of the form lines can be carried out 
within fairly high limits of accuracy, and the resulting maps are certainly 
good enough to obtain the necessary information on communications possibil 
ities. In this respect, particularly in forest operations in the developing coun 
tries, communications may involve floating or rafting logs on rivers or lagoons, 
a consideration of logging roads, railways or hauling tracks in swamp country, 
a consideration of main extraction roads in various types of forest and of cable 
ways or timber chutes in mountain country. All these factors have to be 
evaluated by the forest engineer in deciding which is the best method of 
extraction in a particular case. This depends on the topography of the area 
and on the size and type of forest trees to be exploited. 
Communications for a finished product, whether this be semi-processed in 
the form of sawn wood or fully fabricated as rolls of newsprint, are often 
decisive in determining the location of a particular forest industry plant. 
Where a large bulk of finished product has to be handled then bulk handling 
facilities, i.e. railway yards or wharves, have to be built and cranes installed 
to handle the finished product. Again an assessment of the aerial photographs 
of the project area usually results in the location of three or four alternative 
sites and it is at this stage, having carried out a study of the raw material 
supplies and of the communications of the area, that the forester engaged in 
the pre-investment survey is in the position of knowing that he has adequate raw 
material supplies and that communications are practicable to selected points. 
Which of these sites he will choose will then depend on the assessment of: 
Other factors 
These in turn will depend on the forest industry or industries concerned. 
I have already mentioned that pulp and paper requires large quantities of 
water and power. In such circumstances an evaluation is made, normally 
using aerial photographs, of the catchments of the project area. These, to 
gether with ground surveys, will determine the water potential of the area