582 



SCIENCE 



[N. S. Vol. XLIX. No. 1277 



fore us a topographic map made by the TJ. S. 

 Geological Sui-vey, say ten years ago, and let 

 it be supposed that this map, at the time it 

 was made, was absolutely perfect. The map 

 is supposed to show the contours, woods, 

 streams, houses and other features that are 

 usually represented on such a map. In the 

 ten years since the map was made, it is rea- 

 sonably certain that some changes have been 

 made by the works of man. It is improbable 

 that natural features would have changed, 

 such as streams, woods and hills, during such 

 a short iperiod. We may assume that new 

 roads have been made, old buildings torn 

 down, or burned, and new ones erected, that 

 wooded areas have been cleared, and that 

 brush or young trees may now be on areas that 

 were bare at the time the original survey was 

 made. In order to test such a map and learn 

 whether it was up to date, it would be nec- 

 essary by the usual methods, to send a sur- 

 veyor into the field to go over the area in great 

 detail. Of course an inspection could be made 

 of an area by driving over it, but many 

 changes might be overlooked by this method 

 of inspection. 



How much simpler and more reliable it 

 would be to send an airplane over the area in 

 question and make a series of photographs. 

 These photographs would show at a glance, 

 the exact areas where changes in the features 

 had occurred, and if the changes were not too 

 complicated it is probable that we would be 

 able to place the new features on the map 

 directly from the photographs. The process 

 would be to fit in the new features between 

 unchanged old features, which of course 

 would also be shown on the photographs. 



PHOTOGRAPHIC PLATE SHOULD BE HORIZONTAL 



In what has been said above, it has been 

 assumed that the photographs have been made 

 with the camera vertical, or, in other words, 

 with the photographic film or plate in a hori- 

 zontal position. It is only in this way that 

 absolutely accurate photographs could be 

 made. If the camera is tilted from the ver- 

 tical at the instant the exposure is made, then 

 there will be a distortion of the photograph so 



far as the map is concerned. If this tilting 

 were known, then the photograph could be 

 rectified and the featiHes shown on the map 

 with the same accuracy as if the plate had 

 been horizontal at the time of the exposure. 

 It is hoped that methods will be developed 

 for holding the camera in a vertical position 

 at the time of exposure. I know of none now 

 in use which is entirely satisfactory. 



CONCLUSION 



I may conclude that airplane surveying can 

 be done now and it undoubtedly has a bright 

 future. Much experimentation must be done, 

 however, before the airplane can be used ex- 

 tensively in high-grade work. 



I feel that the airplane can now furnish 

 maps of a low order of accuracy so far as scale 

 and position of features are concerned, which 

 will be of considerable value in many branches 

 of industry and commerce. They will un- 

 doubtedly be extensively used in unmapped 

 areas in this and other countries in the very 

 near future, for reconnoissance surveys and 

 maps. But I hope they may be of great use in 

 more accurate work. 



I can pledge the Coast and Geodetic Survey, 

 so far as its limited resources will allow, to 

 take its part in making such tests by airplane 

 as may be feasible in connection with survey- 

 ing and mapping. 



E. Lester Jones 



U. S. Coast and Geodetic Survey 



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