Interpolation of Contour lines | Contour lines | How to draw contour map | Purpose of contour maps

This video is about to describe the Grid / box method of drawing contour lines. procedure to draw contour lines of a given terrain with spot heights with respect to any reference.

Interpolation of contour lines is described to make the contour lines more precise and accurate to reflect the correct spatial area of the terrain.

Definition of Contour line.
a line (as on a map) connecting the points on a land surface that have the same elevation

Uses of contours maps
Contours provide valuable information about the nature of terrain. This is very important for selection of sites, determination of catchment area of a drainage basin, to find inter-visibility between stations etc. Some of the salient uses of contours are described below

Nature of Ground
To visualize the nature of ground along a cross section of interest,

To Locate Route
Contour map provides useful information for locating a route at a given gradient such as highway, canal, sewer line etc.

Inter-visibility between Stations
When the inter-visibility between two points can not be ascertained by inspection of the area, it can be determined using contour map.

To Determine Catchment Area or Drainage Area
The catchment area of a river is determined by using contour map. The watershed line which indicates the drainage basin of a river passes through the ridges and saddles of the terrain around the river. Thus, it is always perpendicular to the contour lines. The catchment area contained between the watershed line and the river outlet is then measured with a planimeter

Storage capacity of a Reservoir
The storage capacity of a reservoir is determined from contour map. The contour line indicating the full reservoir level (F.R.L) is drawn on the contour map. The area enclosed between successive contours are measured by planimeter .The volume of water between F.R.L and the river bed is finally estimated by using either Trapezoidal formula or Prismoidal formula.