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The process of drawing contours with the help of height of various points on the map marked by spot heights, bench marks and triangulation stations is known as interpolation of contours. Following steps are necessary for interpolation of contours :

(i) First of all mark heights of various points on the map. It is worth remembering that large the number of points, better will be the interpolation.

(ii) Note the points having maximum and minimum heights. The difference between maximum and minimum heights is known as range of elevation.