TOPOGRAPHY. 57 
those States, but for that in other States in which cooperation was not 
being carried on. This change was gradually extended to other 
regions, so that at the close of the first decade of the existence of the 
organization the scale and methods of work had been elaborated until 
they had reached practically their present status. 
The earlier topographic mapping of the Survey was subjected to 
some criticism on account of lack of refinement in detail. It was a 
question of judgment whether the appropriation should be expended 
in accurately mapping a limited area or in making reconnaissance 
surveys over a more extended area. The less accurate maps were less 
expensive, and served a useful purpose in establishing the value of 
topographic surveys. The results have proved the wisdom of a policy 
whereby the people were gradually educated to the use of refined and 
detailed maps, while Congress learned to appreciate the cost and the 
comparative slowness with which accurate surveys would be prosecuted 
over so vast a territory as that of the United States. Had fewer 
square miles been mapped annually in the early years, but with the 
accuracy attained at present, it is doubtful if Congress would have 
continued to maintain the organization. As it was, valuable results 
were rapidly put forth, and in time it has been possible to supersede 
the older reconnaissance maps with more detailed maps, which serve as 
a basis for satisfactory delineation of the underlying mineral resources. 
As the topographic work steadily advanced, not only in scope, but 
in accuracy, it was found desirable to obtain from Congress authority 
to run careful spirit-level lines and to establish bench marks for per- 
manent record of elevations upon the ground, and also to carry on 
control by triangulation or traverse with greater accuracy and to mark 
the positions more permanently than had been possible without statu- 
tory authority. Accordingly, on June 11, 1896, an act was approved 
which provided that "elevations above a base level located in each 
area under survey shall be determined and marked on the ground by 
iron or stone posts or bench marks," etc. Thereafter it was possible 
to provide for the running of careful spirit levels over all the areas 
under survey and to extend the amount of spirit leveling, thereb} 7 
securing more accurate location of contours. Since that act was 
passed the topographic mapping has reached as high a degree of detail 
and quality as seems desirable for the scales adopted. 
The features exhibited on the topographic maps of the United States 
Geological Survey are: 
1. Hydrography, or water features, as ponds, streams, lakes, swamps, 
etc., which are printed in blue. 
2. Hypsography, or relief of surface, as hills, valleys, and plains, 
which are printed in brown. 
3. Culture, or features constructed by man, as cities, roads, villages, 
and the names and boundaries, which are printed in black. 
