Topography

Topography is a general term in geography, derived from the Greek "topos" (place) and "graphein" (to draw), and refers to the lie of the land, or various other characteristics of Physical geography in a region; this is usually expressed in terms of the elevation, slope, and orientation of terrain features. The understanding of these features is an integral aspect of geography, encompassing the practice of cartography, surveying, and GIS. Maps are the most common communication tool for topographic information.

Relief often used to refer to the third dimension of a map whether in actuality (as in a "raised relief" map, or drawn, as with contours, hachures or shading) or the territory it describes. 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.

The understanding of topography is critical for a number of reasons. In terms of environmental quality, agriculture, and hydrology, understanding the topography of an area enables the understanding of watershed boundaries, drainage characteristics, water movement, and impacts on water quality. Complex arrays of topographic data are used as input parameters for hydrology transport models (such as the SWMM or DSSAM Models) to allow prediction of river water quality.

Understanding topography also impinges on soil conservation, especially in agriculture. Contour plowing is an established practice of enabling sustainable agriculture on sloping land, and is the practice of plowing along topographic lines.

Topography is critical militarily because it determines the ability of armed forces to take and hold areas, and to move troops and material into and through areas.

Topography is important in determining weather patterns. Two areas in proximity to each other geographically may differ radically in characteristics such as precipitation because of elevation differences or because of a "rain shadow" effect.

Tectonic processes and erosional processes are the determiners of topography. Tectonic processes such as orogenies cause land to be elevated, and erosional (and weathering) processes cause land to be worn away to lower elevations.

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