SOUTH AND EAST AFRICA. 47 



Air Force, in connection with Sir Pierre Van Rijneveld's great 

 Cairo-to-Cape flight in 1920. In desert and semi-desert country almost 

 natural aerodromes are sometimes found ') requiring very little 

 preparation beyond putting in large white circles which may be 

 seen from the air and flags and small white patches to mark the 

 boundaries. In bush country the trees and scrub have to be cut 

 down and burnt and stumps removed, ant hills destroyed and the 

 whole surface levelled and made as firm as possible, since soft 

 ground is very bad for landing and taking off. All large trees near 

 the boundaries are also cut down. Having done all this it is neces- 

 sary to instal permanently a small gang of natives for keeping down 

 vegetation which would otherwise soon obscure the landing circle. 

 As to the cost of aerial surveys there is as yet very little to go 

 upon. It is however very much less that that of ordinary surveys. 

 Under the conditions obtaining in Egypt, which are very similar 

 to those in the areas under consideration, it is estimated that the, 

 cost per square mile of map on a scale of 1 : 2500 would vary 2 ) 

 from 5 to 15, whereas the cost of surveying the same ground 

 by theodolite and plane table varies from 10 to > 1000 per 

 square mile. 



3. SELECTION AND PREPARATION OF CAMP SITES. 



In selecting a site for a camp regard must bo had to several 

 important matters. In the first place the camp should always be 

 pitched on high ground having just enough slope to carry off water; 

 never near the bank of a river or standing water and never too 

 close to native villages or dense bush. AVhere there are shady trees 

 about it is a great advantage to camp under one, but sight i 

 not be lost of the fact that in the summer months trees often har- 

 bour venomous snakes. 



The camp must of course be favourably situated with regard t< 

 water, fuel supply, and irra/ins when travelling with animals. 



It is always well during the winter months to safeguard the 

 camp from grass fires by burning a fire ring about 25 yards wide, 

 round it, taking care that tlii> i- done under j. roper sujM-rvi^ion 80 

 as not to set the surrounding veld on fire. \Vhen the rains IP 

 it is very necessary to have a properly graded drainage trench dug 

 all round the camp, and tents must moreover be ditched so as to 

 prevent water from running under them. 



Geographical ! September, 1920. 



2) Geograj.lii. .il .iMiirnal, June, 1920. 



