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About Topographic Maps

An explanation and potted history of topographic maps and USGS Quads

What is a Topographic Map?

A topographic map is a type of map that represents changes in elevation. Traditional definitions require a topographic map to show both natural and man-made features. A topographic map is typically published as a paper map series, made up of map sheets that combine to form the whole map. When used in a digital system, the whole topographic map can be presented seamlessly. A contour line is the most common way to represent elevation on a topographic map but other techniques such as relief shading compliment the visual effect.

Historically, topographic surveys were prepared by the military to assist in battle and defensive planning. It is also fundamental to the accuracy of artillery, thus the name and history of the United Kingdom's government agency and map publisher; the Ordnance Survey. As such, elevation information and man made features was (and still is) of vital importance to any military planner.

A concise definition of a topographic map as provided by The Canadian Centre for Topographic Information is: ATopographic maps topographic map is a detailed and accurate graphic representation of cultural and natural features on the ground.

Technically, the study or discipline of topography, while interested in relief, is actually a much broader field of study which takes into account all natural and man made features of terrain.

The various features shown on the map are represented by conventional signs or symbols. For example, colors can be used to indicate a classification of roads. These signs are usually explained in the margin of the map, or on a separately published Map Legend

Topographic maps are also commonly called contour maps or topo maps. In the United States, where the primary national series is organized by a strict 7.5 minute grid, they are often called topo quads or USGS quads.

Topographic maps conventionally show topography, or land contours, by means of contour lines. Contour lines are curves that connect contiguous points of the same altitude. In other words, every point on the marked line of 100 m elevation is 100 m above mean sea level. These maps usually show not only the contours, but also any significant streams or other bodies of water, forest cover, built-up areas or individual buildings (depending on scale), and other features and points of interest.

The United States Geological Survey (USGS), a civilian Federal agency, produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest (both in terms of scale and quantity) and best-known topographic series is the 7.5-minute or 1:24,000 quadrangle. This scale is virtually unique to the United States and offers a convenient relation to customary units of measure where 1 map inch equals 2,000 actual feet.

Topographic maps have multiple uses in the present day: In industry, any type of geographic planning or large-scale architecture; such as mining and other earth-based works; and recreational uses such as hiking or otherwise any exploration of wilderness and rural areas.