What are hachured contour lines?


Hachured contour lines are circular lines on a topographic map that have little teeth, or hash marks, that point into a depression that is below a higher elevation. Also known as depression contours, common geologic features indicated by hachured contour lines include craters and cones of volcanoes.

Concentric circles with hachure marks in the middle denote a hill with a depression on top. For instance, the top line of concentric circles could indicate 1,397 feet above sea level. The next, inner contour line could indicate an elevation of 1,200 feet above sea level. The next innermost circle could be 1,000 feet high. The two contour lines inside the line of 1,397 feet would have hachures to indicate lower elevations inside a high elevation on the map. Small hachure marks point towards the inside of the concentric circles.

Sometimes, hachure contour lines repeat the previous elevation simply because cartographers denote a downslope rather than an upslope. Elevations that decrease, rather than increase, within concentric circles are indicated by red dots with specific elevation numbers. Nearby points with definitive elevations have blue dots to mark higher points than those of the depression.

The term hachure comes from the French word "hacher," which means "to chop up" or "to hatch," as with a hatchet. This connotes small lines that cut a larger line into smaller pieces on a topographic map.

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