482 THE POPULAR SCIENCE MONTHLY. 



whole domains, and that outside of Europe the United States 

 claim first attention by their grand topographic works. 



Similar surveys are also in progress in the principal colonies of 

 the European powers, such as India, Canada, Algeria, Tunis, etc. 

 The scale of the maps varies from 1 : 2,000 to 1 : 420,000. 



According to Lowinsin, seventy per cent of the area of Europe 

 has had a fairly satisfactory topographic survey ; and of the land 

 area of the world, about twenty-seven per cent has been surveyed 

 more or less accurately. Bartholomew estimates that only one 

 seventh of the whole land surface of the globe has been exactly 

 surveyed. He publishes an instructive map exhibiting the area 

 of topographic surveys, both exact and general, and of geographic 

 surveys, both fairly reliable and approximate or hypothetical.* 



Most European topographic maps were made, primarily, for 

 military purposes, under the supervision of military officers, and 

 secondarily for the scientist and statesman only. In the United 

 States the necessities of the geologist developed the first interior 

 surveys, and they are now being carried forward under the direc- 

 tion of the Geological Survey, and, along the ocean borders, by 

 the Coast and Goedetic Survey. 



The methods employed are the same in all topographic surveys, 

 in respect to the two essential divisions of work, viz., location 

 of points of control and sketching in of contours, streams, culture, 

 etc. The minor methods of procedure differ in details within these 

 two divisions ; but geometrically located points of control are in 

 all cases obtained, and the contours, roads, streams, and all fea- 

 tures shown on the map are sketched in, whether the located points 

 of control are ten inches or a thousand feet apart. Usually it is 

 only the features sketched that appear on the map, as the geomet- 

 rically located points that control the sketch are mathematical 

 points. If desired they can be represented by conventional signs. 



The first contoured topographic maps of the United States for 

 geologic purposes were on the scale of 1 : 250,000 (four miles to the 

 inch), with contour intervals of two hundred to two hundred and 

 fifty feet ; but the necessities of science and the demands of the pub- 

 lic called for a more detailed map, and the scale of 1 : 125,000 (two 

 miles to the inch) was adopted. This was again enlarged in cer- 

 tain regions to 1 : 62,500 (one mile to the inch). The topographic 

 maps of the Geological Survey are now being made, in the rough- 

 er mountain region and thinly populated areas:, on the 1 : 125,000 

 scale, with contour intervals of from ten to one hundred feet, and in 

 the more valuable, economic, and thickly populated areas, on the 

 1 : 62,500 scale, with contour intervals of from five to one hundred 



* John George Bartholomew. Scottish Geographical Magazine, vol. vi, 1890, pp. 294, 

 295, and map. 



