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STATES 
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gradually 
versed by a few shallow gullies. On the map each 
features as represented,: directly 
sketch, by; contour lines. 
The contour interval, or the vertical distance in feet bel 
one contour and the next, is stated at the bottom of each 
This interval differs according to the topography of th 
mapped; in a flat country it may be as small as 1 foot: 
* * i/ w v w j 
mountainous region it maybe as great as:250 feet C< 
contour lines, every fourth or fifth one, are made hea 
the others and are accompanied by figures showing alti 
points—such as road corners, sum 
marks—are also given on the} 
ench 
