Cartographic relief depiction
From Wikipedia, the free encyclopedia
Terrain or relief is an essential aspect of physical geography, and as such its portrayal presents a central problem in cartography, and more recently GIS and 3D Visualization.
The most obvious way to depict relief is through physically molding the map, thus molded or carved solid terrain models and molded-plastic raised-relief maps.
On flat paper maps, terrain can be depicted in a variety of ways, outlined below:
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[edit] Contour lines
Contour lines or Isohypses are isolines showing equal elevation. This is the most common way of numerically showing elevation, and is familiar from topographic maps. Most 18th and early 19th century national surveys did not record relief across the entire area of coverage, calculating only spot elevations at survey points. The United States Geological Survey (USGS) topographical survey maps included contour representation of relief, and so maps that show relief, especially with exact representation of elevation, came to be called topographic maps (or "topo" maps) in the United States, and the usage has spread internationally.
[edit] Hypsometric tints
Hypsometric tints are a variant on contour lines. They depict ranges of elevation as bands of graduated color. The most common color scale runs from greens in the lowlands through yellows and browns to greys and whites on alpine peaks.
[edit] Hachures
Hachures are an older mode of representing relief. They show orientation of slope, and by their 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.
[edit] Shaded relief
Shaded relief or hill-shading simulates the cast shadow thrown upon a raised relief map, or more abstractly the shadow of the sun. The conventional angle of the light source for such models (upper left) makes such depictions in the northern latitudes non-represeetnative of actual light/shadow patterns. Traditionally drawn with charcoal and other traditional media, shaded relief is today almost exclusively computer-generated, with a resulting different look and feel. Much work has been done in digitally recreating the work of Swiss master Eduard Imhof, widely regarded as the master of manual hill-shading technique and theory.
Portrayal of relief is especially important in mountainous regions. The Commission on Mountain Cartography of the International Cartographic Association is the best-known forum for discussion of theory and techniques for mapping these regions.
