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A hachure is a type of line or series of lines drawn on a map to denote the shape and slope of a land feature. These lines are able to convey the direction as well as the relative steepness of a slope but are somewhat inexact in their ability to convey precise information on elevation and slope in the way that contour lines are. The term hachure is from the French language and means "hatch" in the sense of a series of lines.
As the science of map-making progressed, map makers struggled to convey information regarding topographical features. The hachure evolved as the most popular method for expressing information about three-dimensional geographical subjects within the constraints of a two-dimensional map or drawing. In the 18th and 19th centuries, this became the accepted convention for depicting slope and contour on maps. Hachure lines fell out of favor and common use with the adoption of contour lines by cartographers in the middle and late 19th century, due to the latter's ability to convey more exact information about slope and elevation of land features.
To describe a slope, hachure lines are drawn running along the slope. They can be seen as drawn from the top of a hill to the bottom. The length of the lines conveys the horizontal distance traversed by the slope, and the density of the lines are able to give information regarding the steepness. Many hachure lines that are drawn very close together show a steep slope, while fewer lines are used to depict a shallow slope.
Several rules for hachures evolved amongst cartographers to ensure consistency in their use and interpretation. Besides the length and frequency of the lines, their thickness also conveys steepness. Thicker or darker lines mean a steeper slope, while thinner or lighter lines mean a gentler or shallower slope. Hachure lines are arranged in rows, the distance between them is constant, and all the lines on a particular row are the same length.
A line joining the hachure lines on the uphill end can also denote the contour of the particular land feature. Several sets of hachure lines drawn in this way can show the shape of a hill as well as the relative steepness of its slopes. This information is inexact, however, and can be interpreted in different ways by different viewers. Contour lines eventually supplanted hachure lines in mapmaking as a much more precise way to denote slope, contour, and elevation and are used almost exclusively on modern maps, although hachure lines are still sometimes used to give a map a historic or old-fashioned look.
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