# State the methods of contour interpolation and explain in brief any one.

State the methods of contour interpolation and explain in brief any one.

Methods of interpolation:-

i) By Arithmetic calculations

ii) By Estimation

iii) By Graphical method

i) By Arithmetic Calculation: This is very tedious but accurate method and is used for small areas where accurate results are necessary.

The contours are interpolated as under:

Suppose A and B are two points at a distance of 30 m and the reduced level of A and B are 25.45m and 27.54m respectively .Taking the contour interval as 1m, 26 and 27 m contours may be interpolated in between A and B. The difference of level between A and B is 2.09m.the difference of level between A and 26m, and A and 27m is 0.55m and 1.55 m respectively. Therefore the horizontal distance between A and 26 m contour =0.55/2.09 x 30m and Between A and 27 m contour =1.55/2.09 x 30m. These distances are then plotted to scale on the map .

ii) By Estimation Method

1. Contour points are estimated by judgment and marked .The contour lines are then drawn through these points.

2. This method is rough and is suitable for small scale works

3. This points located by judgment is not accurate as located by arithmetic calculations

iii) By Graphical Method

Several lines are drawn parallel to each other on a tracing paper say at an interval of 0.5 m. in fig the bottom most line represent an elevation of 80.00m and if it is required to interpolate contour of 81.5,82 and 82.5 between a line PQ of an elevation of 80.00m and 84.00 m then keep the tracing paper on the line in such a way that point P may lie on a parallel representing an elevation of 80.00 m. Now, rotate the tracing paper on drawing in such a way that point Q may lie parallel representing an elevation of 84.00m. The points at which the parallel representing 81.5, 82.0 and 82.5m (shown by X, Y, Z in fig.) may now be pricked through the position of the contour points on line PQ.

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