12 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
(a) Maps on a very small scale may be called generalized maps, 
and, though showing topographic features as fully and completely 
as the scale will permit, are still not properly,topographic but gen- 
eralized maps. 
Maps on very large scales, on the other hand, though sometimes 
containing curves of equal altitude or contours, are yet rather dia- 
grams or plans than topographic maps. 
The topographic map requires a scale somewhere between the 
small scale generalized map and the very large scale plan. 
(b) The class to which any given map must be referred further 
depends upon its purpose. Ifthe purpose is to exhibit the geologic 
structure, it is a geologic map; if designed for military purposes, a 
military map; if for nautical purposes, a nautical map—or, as it is 
called, a chart—and if for exhibiting the topography, a topographic 
map. If a topographic map is colored to exhibit the geologic 
structure of the region shown, it is no longer a topographic but a 
geologic map, ete. Most of the maps of the Coast Survey, though 
exhibiting more or less topography, would not be classed with topo- 
graphic maps, but with charts, being designed for nautical pur- 
poses. 
(ec) The features to be exhibited on a map, in order that it may 
be classed as topographic, are (1) the relief, (2) the drainage, in- 
cluding in this term the whole water system of ponds, lakes, swamps, 
streams, etc., and (3) the culture, this term implying the works of 
man of such size or importance as to warrant their being classed as 
topographic features. What features are topographic depends upon 
the scale of the map. 
(d) With respect to accuracy we shall have topographic maps 
and topographic sketches. A topographic sketch controlled by 
locations is a topographic map; not so controlled, it remains a 
sketch. 
This communication was discussed by Messrs. G. Toompson, H. 
Farquuar, R. D. Mussty, and the author. 
