Rules and Terms for Using Contour Lines

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Rules for Using Contour Lines

Connects all points of equal elevation

Separate points of higher elevation (uphill) from points of lower elevation (downhill)

Contour interval: Index contours are printed as heavier and darker lines, usually every 5th contour line and are labeled with elevation numbers in feet or meters

Contour lines always close or come back to starting point so that they form continuous loops and irregular loops

CONTOUR LINES DO NOT CROSS

Can only merge in the case of a vertical slope such as a cliff

Evenly spaced contour lines suggest a uniform slope

Closely spaced contour lines suggest steep sloves while widely spaced contours record gentle slopes

a series of concentric, closed contour loops will define a hill or mountain

HACHURES (short dashed lines at right angles to one side of the contour line) indicate a closed depression

Downward streams will form a "v" pattern where they cross the stream and the "v" will point upstream (uphill)

A "v" pattern points downhill, the contour lines are defining a ridge

Other notes:

Relief: the difference between high and low areas of a map

Local relief: difference in elevation between 2 areas being compared

Total relief: difference in elevation between the highest and lowest areas on the map

Gradient: the expression of the steepness of a slope. Determined by dividing the relief between 2 points of interest by the distance measured from the map and is expressed in feet per mile or in meters per km