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Hachures () are an older mode of representing relief. They show orientation of slope, and by their thickness and overall density they provide a general sense of steepness. Being non-numeric, they are less useful to a scientific survey than contours, but can successfully communicate quite specific shapes of terrain. They are a form of
shading Shading refers to the depiction of depth perception in 3D models (within the field of 3D computer graphics) or illustrations (in visual art) by varying the level of darkness. Shading tries to approximate local behavior of light on the ob ...
, although different from the one used in shaded maps. Hachure representation of relief was standardized by the Austrian topographer Johann Georg Lehmann in 1799. Hachures may be combined with other ways of representing relief, such as shades, the result being a shaded hachure map; an example of such a map is the ''
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'' of Switzerland.
Emil von Sydow Emil von Sydow (15 July 1812 – 13 October 1873) was a German military officer, geographer and cartographer born in Freiberg, Saxony. Prior to 1843 he was a geography instructor at the military academy in Erfurt, afterwards being appointed as a ...
designed maps with coloured hachures: green for lowlands and brown for highlands.


Overview

Hachures are strokes (short line segments or curves) drawn in the direction of the steepest slope (the
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direction). Steeper slopes are represented by thicker, shorter strokes, while gentler slopes are represented by thinner, longer and farther apart strokes. A very gentle slope or a flat area, like the top of a hill, is usually left blank. The hachures are traditionally monocolour, usually black, gray or brown. Using two complementary colours for the hachures on a neutral background colour (e.g. black and white lines on gray map colour) would give a shading effect as if the relief were illuminated. Hachures can also be used to represent water features such as coastlines or lakes, in which case they consist of fine parallel lines.


Rules

In representing relief with hachures on a map, six rules are to be followed, according to G.R.P. Lawrence (1979): # The hachures are drawn in the direction of the steepest gradient. # The hachures are arranged in rows perpendicular to their direction. # The length and thickness of each stroke represents the drop in height along its direction: a short and thick stroke represents a short and steep slope, while a long and thin stroke represents a long and gentle slope. # The strokes are spaced at an equal distance inside a row. # The strokes have the same thickness inside a row. # If the map is illuminated, strokes are thinner and farther apart on the illuminated side. The Swiss cartographer
Eduard Imhof Eduard Imhof (25 January 1895 – 27 April 1986) was a professor of cartography at the Swiss Federal Institute of Technology, Zürich, from 1925 to 1965. His fame, which extends far beyond the Institute of Technology, stems from his relief shadi ...
set 5 similar rules: # Hachures follow the direction of steepest gradient # Hachures are arranged in horizontal rows # Hachure length corresponds to the local horizontal distance between assumed contours of a certain interval # Hachure width is thicker for steeper slopes # Hachure density remains constant throughout the map area. If the illumination is vertical, rule 5 is kept; in the case of oblique illumination, it is dropped. The rules above are to be obeyed for large-scale maps. If the map being drawn is a small-scale map (less than 1:500 000 according to Imhof), rules may be relaxed in order to obtain a more suggestive representation. Hachures are still used today on Large Scale maps to show slopes and on British Ordnance Survey Maps and also in various countries toposheets to show Road and Railway Cutting and Embankments. On British OS Maps they have become long triangles with the short base at the top, and always pointing downwards. Embankments are further identified by having a line around them.


References

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External links


Desktop Hachure Maps from Digital Elevation Models
* ttp://www.geog.port.ac.uk/webmap/hantsmap/hantsmap/ordnce6/oss42.htm Map of part of Hampshire, 1810sbr>Map of Hampshire, 1826
Map types Physical geography