Each contour line represents one elevation. Contour lines never cross. In the extremely rare case of an overhang, contour lines would cross, but the hidden contours are dashed. The more rugged the topography in an area, the larger the contour interval that is required for the map. The contour interval is generally given in the legend of the map.
Every fifth contour is printed darker.
These lines are called index contours . Closely spaced contour lines represent steep slopes. Widely spaced contour lines represent gentle slopes. Examples of closed depressions are sinkholes and craters, or other bowl-shaped depressions. A series of contentric contour lines in a rough circle represents a hill.