V 
DESCRIPTION OF THE TOPOGRARI 
The United States Geological Survey is making 
a topographic map of the United States. This 
work has been in progress since 1882, and about 
three-tenths of the area of the country, excluding 
■** 
outlying possessions, has been mapped. The map- 
ped areas are widely scattered, nearly every State 
being represented as shown on the progress maps 
accompanying each annual report of the Director. 
This great map is being published in atlas sheets 
of convenient size, which are bounded by parallels 
and meridians. The four-cornered division of 
land corresponding to an atlas sheet is called a 
quadrangle . The sheets are of approximately the 
same size: the paper dimensions are 20 by IGi 
inches; the occupies about 17 £ inches of 
height and 11 £ io 16 inches of width, the latter 
varying with latitude. Three scales, however, are 
employed. The largest scale is 1:62500, or very 
nearly one mile to one inch; i. e., one linear mile 
on the ground is represented by one linear inch on 
the map. This scale is used for the thickly settled 
or industrially important parts of the country. 
For the greater part of the country an intermediate 
scale of 1:125000, or about two miles to one inch, 
is employed. A third and still smaller scale, of 
1:250000, or about four miles to one inch, has 
been used in the desert regions of the far West. 
A few special maps on larger scales are made of 
limited areas in mining districts. The sheets on 
the largest scale cover 15' of latitude by 15' of 
longitude; those on the intermediate scale, 30' of 
latitude by 30' of longitude; and those on the 
smallest scale, 1° of latitude by 1° of longitude. 
The features shown on this map may, for con- 
venience, be classed in three groups; (1) water , 
including seas, lakes, ponds, rivers and other 
to g q^nrvms. etc. : (2) relief* including 
times, are shown, not by i| 
dots and dashes. Ponds, 
part of the year are sh<| 
lines. Salt-water marshes 
ruling interspersed with 
water marshes and swai 
broken horizontal lines. 
Relief is shown by 
Each contour passes thri| 
same altitude. One win 
the ground will go neithj 
but on a level. By the 
are the shapes of the plal 
shown, but also the elevd 
seaeoast itself is a contoutl 
of elevation being mean 
line at, say, 20 feet above 
would be the seaeoast if tf 
land to sink 20 feet. Sij 
the valleys and forward ;j 
and spurs. On a gentle a 
far from the present coat 
J- 
slope it is near it. Thus 
tour lines far apart on til 
slope; if close together, a 
contours run together in < 
vertically under the one | 
cliff. In many parts of tl 
or hollows with no outlets, 
surround these, just as th<| 
small hollows known as si 
by hachures, or short das| 
curve. The contour Intel 
tance in feet between one 
stated at the bottom of ee 
varies according to tin 
manned : in a flat countr 
