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features are shown and explained below. Variations appear o 
some irlier maps, and additional features are represented o| 
some special maps. ■ . ,<j ' fr 
8p6C1c^Ji ma j;o* j 
All the water features are represented in blue, the small* 
streams and canals by single blue lines and the larger stream 
the lakes, and the sea by blue water lining or blue tint Intel 
mittent streams—those whose beds are dry for a large part 
the year—are shown by lines of blue dots and dashes. 
Ltenei is shown by contour lines in brown which on 
maps are supplemented by shading showing the effect of ligj 
thrown from the northwest across the area represented for iij 
purpose of giving the appearance of relief and thus aiding i 
the interpretation of the contour lines. A contour line 
scuts an imaginary line on the ground (a contour) every pa! 
of which is at the same altitude above sea level. {Such a lb 
* 
could he drawn at any altitude, hut in practice only the coi 
tom’s at certain regular intervals of altitude are shown. 
b ------- - - -- 
line of the sea coast itself is a contour, the datum or zero of alt 
tude being mean sea level. The 20-foot con tout would be th 
shore- line if the sea should rise 20 feet. Contour lines sho 
the shape of the hills, mountains, and valleys, as well as ihe¬ 
al thud e. Successive contour lines that are far apart on t! 
map indicate a gentle slope; lines that are close together imjj 
cate a steep slope; and lines that run together indicate a cliff. 
The manner in which contour lines expo tltitude, fori 
and grade is shown in the figure below. 
