11/13/2022 0 Comments Contour intervalFor example, suppose there are 5 lines between two index lines. Step 4: Take the number of lines acquired in the previous step and multiply it by 1. Step 3: Count the number of non-index contour lines that exist between the two index contour lines that were chosen for the contour interval calculation in the first step. Subtract the upper elevated line reading from the lower elevated line reading to get the difference. Step 2: Now compute the difference between the two index contour lines chosen from a map. Step 1: First, find two index contour lines that are identified with an elevation. The contour intervals are calculated as follows: Maps typically count five contour lines, including the next index line, from one index line to the next. Begin by counting the contour lines from one index line to the next. #CONTOUR INTERVAL HOW TO#To Understanding how to compute the contour interval is a useful skill to have. Determine the difference in elevations between the two.įor example, if the uphill height is 1,000 feet above sea level and the lowest elevation is 800 feet above sea level, the elevation difference is 200 feet. The highest number represents the steepest ascent. The elevation of these index lines will be marked.ĭetermine the heights of two adjacent index lines. Each fifth contour line, indicated as a heavier or darker line on most maps, is an index line or index contour. Understanding how to compute the contour interval is a useful skill to have. The contour interval on the map is normally identified by a map legend, but sometimes only a portion of a map is visible. If time is the limiting factor, then it may be best to focus on areas with the highest possible levels of detail. In flat or urban areas, the contour interval will be smaller because features are more spread out and easier to distinguish. In mountainous terrain, the most interesting regions will be higher and where valleys and ridges protrude far below the surface. In areas with dense vegetation, it may be difficult to distinguish between two different profiles of a single hill. In areas with dense cloud cover, the contour interval will be lower than in areas with high above-ground features. The size of the area being mapped has an effect on how closely a contour interval should approximate actual elevation measurement, but is not an absolute requirement. The resulting interval will represent an idealized distance based on map scale, but will be very close in reality due to the approximate nature of the technique. The same process is used to determine the total number of degrees measured on each degree’s worth of latitude and longitude. To obtain an actual value, first calculate the length of each degree on the map, then multiply that length by 360 to determine the total length measured along one degree’s worth of latitude or longitude. The contour interval of a map scale represents an idealized distance between two points on a surface. Factors Affecting the Selection of Contour IntervalĬontour interval is affected by the contour interval of the map scale, the area being mapped, the topographic features being mapped and time and resources available. For a 1:24,000 map scale, the standard contour interval is 20 feet. It is possible to determine the contour interval when it is not provided on the map. The contour interval is specified on the right-hand bottom side of each map. Contour intervals are assumed based on the size of the area to be mapped.
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