The conventional signs used to represent these 
town and explained below. Variations appear on 
maps, and additional features are represented on 
naps. 
or features are represented in blue, the smaller 
Inals by single blue lines and the larger streams, 
the sea by blue water lining or blue tint. Inter¬ 
ns—those whose beds are dry for a large part o 
shown by lines of blue dots and dashes, 
iiown by contour lines in brown, which on some 
iplemented by shading showing the effect of light 
the northwest across the area represented, for the] 
iving the appearance of relief and thus aiding in 
jition of the contour lines. A contour line repre 
ginary line on the ground (a contour) every par 
t the same altitude above sea level. Such a lineL 
|wn at any altitude, but in. practice only the con-p 
in regular intervals* of altitude are showu. The 
K)ast itself is a contour, the datum or zero ot alta- 
ean sea level. The 20-foot contour would be the 
the sea should rise 20 feet. Contour lines show 
the hills, mountains, and valleys, as well as their 
accessive contour lines that are far apart on th 
e a gentle slope; lines that are close together imli- 
f lope; and lines that run together indicate a cliff, 
er in which contour lines express altitude, form, 
shown in the figure below. 
l«W_97 
Mexico, are 
;y to be used in the publication of maps on a scale of 
inch=nearly 2 miles), with a contour interval of 25 to 
it. 
>pographic survey of Alaska has been in progress since 
area has now been mapped. 
