Contour lines on standard US Geological Survey topographic maps are brown - e xcept on the surfaces of glaciers, where the contour lines are blue. (The short lines sticking out of the contour lines are called hachures, hatch marks, or tick marks.) Depressions that have no outlet are signified by closed contours with short lines that stick out of them and point toward the center.Circles that are closed contours generally signify hills.(However, in the rare case of a vertical cliff showing up on a topographic map, contour lines along the cliff may appear to join together into a single line.) Contour lines do not intersect each other, because a point on the surface of the earth cannot be at two different elevations. On a map with a 40-foot contour interval, the vertical distance between two contour lines that are next to each other, is 40 feet, regardless of the horizontal distance between the two lines on the map.
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