56 SCIENCE IN AFRICA 



Stages of aerial survey is very considerable, and since the cost of 

 draughtsmen capable of contouring from air photographs may 

 be as high as, or higher than, that of the plane-tabler who works in 

 the field, it is clear that claims for extreme rapidity or lower costs 

 of air survey should be made with caution. The perfecting and 

 speeding up of a mechanical technique for contouring from air 

 photographs may be hoped for before many years pass, and should 

 then alter the balance in favour of air work. Another and more 

 recent review of methods of air survey and the apparatus at present 

 available is given in the second Report of the Air Survey Com- 

 mittee (1935). This Committee grew from a suggestion of the 

 Army Council in 1919, and now includes representatives of the 

 War Office, Air Ministry, Admiralty, Ordnance Survey, and 

 Department of Scientific and Industrial Research. An appendix 

 to their most recent report analyses the cost of air survey based on 

 the future existence of an air survey organization on a permanent 

 basis, undertaking operations on a large scale. In undeveloped 

 country where land transport is difficult, the cost of survey is esti- 

 mated for an area of 1,000,000 square miles, which would entail six 

 years devoted to air photography. The total cost, including photo- 

 graphic material, but not the production of maps, works out at 

 23s. per square mile. For smaller areas this cost would be con- 

 siderably more, rising to i8os. per square mile for an area of 500 

 square miles, and it would be much higher in urbanized areas. 

 At present the situation with regard solely to the production of 

 maps may be summed up in the words of Brigadier MacLeod who, 

 as former Chairman of the Air Survey Committee, is by no means 

 an antagonist: 'Wherever there are sufficient communications, or 

 there is a reasonable choice between the two methods as alterna- 

 tive, ground methods are, from the purely survey point of view, 

 almost always better for a given standard of accuracy.' 



Air survey provides, however, not only topographical maps 

 drawn from the photographs, but the photographs themselves, and 

 this introduces the second aspect of the question, namely air photo- 

 graphy as a means of showing the natural resources of a country. 

 In choosing routes for railways and roads, sites for townships and so 

 forth, air photographs have already saved much laborious ground 

 work in some places. In addition to this the distribution of vegeta- 



