June 20, 1919] 



SCIENCE 



577 



features and the elevations by contours of 

 hills, ridges, valleys, etc. These are the maps 

 of class three, mentioned previously. Some of 

 the 40 per cent, of the surveyed area will have 

 to be resurveyed because the original work 

 was done many years ago when methods were 

 not as refined as they are at present and the 

 demands of map users were not as exacting as 

 they are to-day. It is safe to say that not 

 over 30 or 35 per cent., or one third of the 

 whole country is adequately mapped. 



The question is, what shall be done with the 

 other 60 per cent. This is a question that is 

 puzzling map makers constantly and no ready 

 solution is at hand provided we insist on hav- 

 ing a map of the whole area within a few 

 years. 



It is possible that here may be a valuable 

 field for the airplane. It is not believed that 

 the airplane unsupported by other surveying 

 can give the final accuracy required in orig- 

 inal survey. But by its means a msp can be 

 made that will be much better than the maps 

 which may be in existence to-day in the areas 

 not topographically mapped. In order that 

 the remaining 60 per cent, of the country 

 might be mapped by airplane it would be nec- 

 essary to have a great amount of tri angulation 

 and traverse run with a view to furnishing 

 the horizontal control for the photographs to 

 be made by the airplane. With this control, 

 it would be possible to fit the photographs on 

 the map into their proper positions. 



CII.VRTS OF THE COAST 



Tlie first class of maps considered here con- 

 sists of charts of the Coast and Geodetic Sur- 

 vey which show the level area immediately 

 along the coast and the water area for some 

 distance out from the shore. The purpose of 

 coast charting is to furnish a safe means of 

 communication by vessels along the coast or 

 in approaching the coast. At present, the 

 methods employed are the usual ones for the 

 topographic surveying of the shore line and 

 the area immediately back of it and the ordi- 

 nary hydrographic methods for the surveying 

 in the water. 



Although the coast line of the United 

 States has been mapped, yet the currents and 

 waves of the oceans cause many large changes 

 in this shore line. For instance Fire Island 

 entrance, Long Island, New York, was changed 

 in position about four miles in fifty years. 

 The changes are so rapid that frequent resur- 

 reys of the coast must be made to f\u:nish ex- 

 act and reliable information to the navigator. 

 It is also necessary to revise the area just back 

 from the coast, for roads are frequently 

 changed in position or abandoned, new ones 

 are established, houses are built or burned, vil- 

 lages spring up, woods are removed or grow 

 over what were vacant fields at the time the 

 map was made, and all of these changes should 

 be shown for the use of the mariner. The 

 question arises as to how such revision shall 

 be made. 



.\IRPLANE SUR^^YIXG WILL DEVELOP 



It is not possible to run many miles with 

 airplane photographs and expect a very high 

 degree of accuracy in the resulting maps. 

 And here I wish to give a word of caution to 

 the advocates of airplane mapping. Too much 

 must not be expected of it. The development 

 of this science will undoubtedly be rather slow 

 for a few years. After it has been developed 

 the methods must, of course, be thoroughly 

 tested before they can be adopted. It is well 

 that this is so, for otherwise haste might cause 

 mistakes which would discredit the method to 

 such an extent that it would take years to 

 recover. 



REMSIOS OF CHARTS BV AIRPLANES 



From the experience of the engineers of the 

 Coast and Geodetic Survey the revision of an 

 area that does not need contouring is almost 

 as exj>ensive and takes almost as much time as 

 the original survey, for it is necessary to make 

 a test of the position of each feature. It is 

 here that the airplane will be of the greatest 

 service, for if a portion of the shore line 

 needs to be inspected with a view to learning 

 whether or not the map of it should be re- 

 vised, we could have a series of photographs 

 made by an airplane along the coast, and a 

 comi)arison of these photographs with the orig- 

 inal map would enable one to locate very defi- 



