10 A MANUAL OF TOPOGRAPHIC METHODS. 



which are of sufficient magnitude to wan-ant representation upon the scale, 

 and to confine the cultural features, that is, the artificial ones, to those which 

 are of general or public importance, leaving out those which are private in 

 their nature. Under this definition the map will represent cities, towns, and 

 villages, roads and railroads and other means of communication (with the 

 exception of private roads), bridges, ferries, tunnels, fords, canals and 

 acequias and boundaries of civil divisions. Fences, property lines, private 

 roads, and other objects of a kindred nature are not represented. The 

 reasons for excluding private culture are apparent. They are, first, because 

 such features are not of sufficient general interest to pay the cost of survey- 

 ing or representing them ; second, because they change rapidly, and, in 

 order to keep the maps up to date, would require constant resurveys and 

 republication, while if the map is not kept constantly up to date, it is mis- 

 leading, and, third, their number and complexity confuse the map and 

 render its more important features less intelligible. 



SIZE OF SHEETS. 



Atlas sheets are designed to be approximately of the same size, 17 5 

 inches in length by from 12 to 15 in breadth, depending upon the latitude, 

 and all those of the same scale cover equal areas, expressed in units of 

 latitude and longitude, that is, each sheet upon the 4-mile scale covers 

 one degree of latitude by one degree of longitude; each sheet upon the 

 2-mile scale, 30 minutes of latitude and longitude, and each sheet upon 

 the 1-mile scale, If) minutes of latitude and longitude. The sheets are 

 thus small enough to be conveniently handled, and, if bound, form an 

 atlas of convenient size. From the fact that each sheet is either a full 

 degree or a regular integral part of a degree, its position with relation to 

 the adjacent sheets and to the area of the country is easy to discover. 



GEOMETRIC CONTROL. 



From the constructive point of view, a map is a sketch, corrected by 

 locations. The work of making locations is geometric, that of sketching is 

 artistic. This definition is applicable to all maps, whatever their quality or 

 character. However numerous the locations may be, they form no part of 



