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A topographic survey is an engineering process used to map the surface of the earth. Topographic assessments differ from other types of surveys in that they are primarily concerned with mapping the shape of the earth, including land contours and elevations, rather than roads. Upon completion of a topographic survey, mapmakers can create a topographic, or contour map. These maps are then used for land planning, construction, mining, and agriculture. Hikers and campers may also rely on a topographic survey map when exploring trails or wilderness areas.
When completing a survey, engineers map the location of both natural and man-made structures within a defined area. This includes bodies of water, land contours, and even buildings or fences. The survey measures the distance between these elements, as well as changes in elevation between each one. A topographic survey generally won't show roads or very small man-made fixtures.
The surveying process begins as topographic surveyors divide an area of land into a grid pattern. Flags or other markers are used to create grid lines, which help surveyors stay organized throughout the process. Engineers may use traditional measuring devices or even satellites and aircraft to measure distance between different points within the grid. These professionals then rely on specialty surveying equipment to measure and calculate elevation changes and angles between each point.
Upon completion of the topographic survey, engineers create a topographical map, which uses contour lines to represent the shape of the earth. When lines are placed close together, this indicates a relatively steep area of land. Lines that are further apart represent shallow or moderate elevation changes. The lines are typically labeled to show the elevation, measured in feet or meters above sea level. To keep the map from appearing too complex, contour lines may be labeled intermittently.
Every fourth or fifth contour line may be darkened to help readers distinguish between different sets of lines. These darker contours are known as guide lines, and are labeled with the land elevation at that point. V-shaped areas within the lines represent streams or rivers, while concentric circles represent hills or mountains. These circles may also represent a pit or void in the earth, so users must read the related elevation information to avoid potential mistakes. The smallest circle within a group of larger circles typically represents the highest or lowest point within the surrounding area, while larger circles show slopes around this apex.