A contour interval within conducting surveys The vertical distance is, or the difference in elevation between two contour lines on the topographic map. There are usually different contour intervals for various maps.
Based on the size of the area that needs to be mapped the contour intervals are assumed. On every map located on the right-hand lower side the contour interval is defined. If the contour interval isn't mentioned in the map, it is calculated as described in the sections below. The most commonly used the contour interval of 20 feet on an area of 1:24,000.
A contour map is composed of contour lines that are located in an area of a particular geographical. To make the contour map easy to comprehend it is not necessary that every contour line is labeled with its elevation reading. These lines marked or labeled are referred to as Index Contour Lines. In the above image The dark lines with readings are the index contour lines. The formula for calculating contour intervals follows as follows:
First, locate two index contour lines marked with an elevation.
Calculate how much difference there is between two index contour line from an image. To calculate this difference subtracting the more elevated line reading from the reading of the lower elevated line.
Now , count the number of non-index lines contour lines that lie between the two contour lines that are selected as index for the contour interval calculation in the 1 St. step.
Lines gathered in the above process is added and rounded to 1. For Ex: If the lines that lie between two index lines is 5. Then , add 1 to 5 and it becomes 6.
The final step is to calculate the ratio from the differences between two index lines (step 2) and the number of lines between two index lines , plus one (step 5.).
The answer we receive after division into the interval of contour of the particular topographic map.
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