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5. From Maps to Models - Background
What is a topographic map (or topo map)? These maps provide a way of showing a 3 dimensional landscape on a 2 dimensional surface. The most distinctive features of a topographic map are the contour lines. Each line represents an imaginary line that connects points that are the same elevation above sea level. Thus, if you walk along a contour line, you would not climb up or down, but stay at the same elevation at all times. USGS maps, the standard topographic map, draw contour lines in brown, labeled at intervals with numbers that represent the elevation above sea level or, in the case of bathymetric maps, the elevation below sea level. Other colors you might find on USGS topo maps are green for vegetation, blue for water features, red for major roads, and grey or black for human developments such as smaller roads, railroads and buildings.
Topo maps are used by most often for navigation so that hikers and explorers can get a sense of the terrain. They are also used by scientists to observe things based on their location and their elevation.
Contour lines are spaced at regular intervals (every 10 feet above sea level is marked with a different line for instance). Thus, the closer 2 lines are together, the steeper the area. Hills can be identified by concentric circles that grow smaller and smaller until you reach the peak of a hill. Depressions such as a dried out pond or the crater of a volcano are generally shown with hatched contour lines.