A contour or a contour line may be defined as a line joining the points having the same elevation above the datum surface. The process of tracing contour lines on the surface of the earth is called contouring and the maps upon which these lines are drawn are called contour maps. The constant vertical distance between any two consecutive contours is called the contour interval. The horizontal distance between any two adjacent contours is termed as the horizontal equivalent and depends upon the slope of the ground. The contour interval depends upon the nature of the ground, scale of the map, purpose and extent of the survey. The contour interval of any survey is inversely proportional to the scale of the map and it should be constant throughout the survey. The following are important characteristics of contours: All points in a contour line have the same elevation. When the contour lines are uniform spaced, it indicates a uniform slope and when they are straight, parallel
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