Contouring

When an elevations and depressions of several points on the ground are needed over widespread areas rather than along a width of field, the levelling exercise called as contouring is resorted to. A line joining the points of similar level (height or RL) is known as a contour line representing the horizontal section of the ground surface at that elevation. The area to be surveyed is commonly divided through a square grid of predetermined size or a system centre points and radial lines and actually plotted on the ground. The RLs of points of intersections are then acquired through usual levelling methods. The contour lines at predetermined intervals are then interpolated and drawn on a map. That map representing a three dimensional information of the ground is known as contour plan.