The ultimate step is the quotient of the difference between the index lines (step 2) and the variety of lines between the 2 index lines plus 1 (step 5). The variety of lines obtained within the above step is taken and added with 1.įor example: if the variety of rows between 2 index lines is 5, then add 1 to 5 which turns into 6. Now calculate the number of non-index lines contour lines between the two indexed contour lines chosen for the contour interval calculated in the 1st step. To take the difference, subtract the upper elevation line with lower elevation line. The calculation of the contour intervals is as follows:įirst, find the two index contour lines which can be labelled with a particular height.Ĭalculate the difference between the 2 selected index contour lines from a map. To maintain the contour map easy and simple to learn, every contour line is not marked by its elevation studying, these marked or labelled lines are identified or known as index contour lines. How to Calculate Contour Interval from Maps?Ī contour map consists of contour lines of a given geographic area. If much less time and resources can be found. If there’s a massive change in ground levels, for example, hills and ponds. If a detailed map is to be prepared for the execution work. Select Low CI like 0.5m, 0.25m, 0.1m or less.įor small scale maps covering a large area of different areas.įor large maps showing details of a small area.įor rough topographic map means for preliminary assessment only. The choice of the contour interval is determined by the survey leader before the beginning of the mapping process based on ground factors as follows. Factors Affecting the Selection of Contour Interval: When the contour interval is not specified within the map, it may be calculated within the following sections, the generally used contour interval is 20 feet for a 1: 24,000 map scale. A contour interval is a vertical distance or a difference in elevation between contour lines in a topographic map, index contour lines are bold or thick lines that appear on every fifth contour line and if the number associated with specific contour lines is increasing, the elevation of the area is also increasing.įor the plotting of region, the contour intervals are assumed, the contour intervals is specified on the right-hand side.
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