46 WAGNER and TREVOR 



villages along the river, either for cash or in exchange for goods. 

 Edible fish can be caught in the river so that fishing tackle can 

 be included in the outfit. 



g. AIR TRAVEL. 



The possibilities of the aeroplane for exploring and surveying 

 remote and inacessible regions are only beginning vaguely to be 

 realised. For making preliminary reconnaisances to obtain some idea 

 of the main features of an unknown tract of country, and of the 

 situation of the rivers, native villages, etc., within it, the aeroplane 

 offers obvious advantages over other methods. It is, however, in 

 actual mapping and surveying that it promises to find its widest 

 and most useful field of application. 



Aerial photographic surveying has of recent years made enormous 

 progress and it may safely be predicted that, in so far as those 

 parts of Africa are concerned of which there are as yet no accurate 

 maps, this will prove by far the cheapest and most satisfactory 

 method of making detailed surveys of areas covered by primary 

 and secondary triangulation. A preliminary geodetic survey is 

 of course necessary so as to have points to tie up with ; the distance 

 between "control" points as they are termed depending upon the 

 accuracy required. 



Surveys from the air will prove especially economical in the vast 

 flat bush and scrub covered tracts that make up most of the central 

 and northern Kalahari, Ovamboland and North-Western and North- 

 Eastern Rhodesia, where ordinary surveying by theodolite and plane 

 table is very costly and laborious owing to the impossibility of 

 getting long sights. Again for mapping an area such as the Ngami 

 Basin with its labyrinth of water ways, and great swamps, a survey 

 from the air is not only likely to prove by far the cheapest and pro- 

 bably the most accurate, but to involve the least risk to those 

 engaged in the work who in ordinary circumstances would be almost 

 certain to contract malaria or black-water fever. 



Apart from ordinary mapping there is no reason whatsoever 

 why preliminary botanical geological and even zoological surveys 

 should not be made from the air. Altogether it looks as though 

 the aeroplane were destined to be the most important factor in the 

 era of African exploration now dawning. 



Suitable landing places and petrol depots will of course have to 

 be established but that this does not offer insuperable difficulties is 

 attested by the excellent work of the NO. 3 Survey Party Royal 



