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contour line

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A contour line is a line that passes through 

points having the same elevation.*

 Elevation from Contours

Elevations of points between contours can be determined by interpolation.

Slope from Contours

The percent slope can also be determined from the contour lines on a topo map.

Determine the slope between the two points on the map.

Rise = 200 - 150 = 50 ft

Run = 2.625 in x 1,000 ft/in

 Eleven (11) characteristics of contour lines
1.Contour lines are continuous. 
2.Contour lines are relatively parallel unless one of two conditions exists. 
3.A series of V-shape indicates a valley and the V’s point to higher elevation.
4.A series U shape indicates a ridge.  The U shapes will point to lower elevation.
5.Evenly spaced lines indicate an area of uniform slope.
Contour Line Characteristics-cont. 
6.A series of closed contours with increasing elevation indicates a hill and a series of closed contours with decreasing elevation indicates a depression.
7.Closed contours may be identified with a +, hill, or -, depression.
8.Closed contours may include hachure marks.  Hachures are short lines perpendicular to the contour line.  They point to lower elevation.

 Contour Line Characteristics-cont.

9.The distance between contour lines indicates the steepness of the slope.  The greater the distance between two contours the less the slope.  The opposite is also true.
10.Contours are perpendicular to the maximum slope.
11.A different type of line should be used for contours of major elevations.  For example at 100, 50 and 10 foot intervals.  Common practice is to identify the major elevations lines, or every fifth line, with a bolder, wider, line.


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