Contour in Surveying

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 Contour 

An imaginary line, on the ground, joining the point of equal elevation above the assumed datum, is called contour.

            




Contour interval

·       The vertical distance between two consecutive contours is known as contour interval.

·       Number of contour line are more in hill as compared to the plains or same contour interval.

·       It depends upon SANAPA

·       Where, S= scale of map, A= Availability of time and fund, N= Nature of ground, E= extend of survey, P= purpose of map and A= amount of permissible error.

·       Contour interval= 20/No of centimeter per km

                            = 50/No of inches per mile

Contour gradient

·       The imaginary line lying throughout on the surface of the earth and preserving a constant inclination to the horizontal.

·       It is either rising gradient or falling gradient.

Horizontal Equivalent

·        The minimum horizontal distance between two consecutive contours.

·        Numerical value of horizontal equivalent in hill is less as compared to the plains.

Interpolation of contours

·        Process of drawing contours proportionately between the plotted ground point or between plotted contours.

Method of contouring

1.     Direct method

2.     Indirect method

1. Direct method:-

·        The contour to be plotted is actually traced on the ground only those point are surveyed which happened to be plotted.

·        This method is slow and tedious.

·        It is generally used for small area and where great accuracy is required.

2. Indirect Method:-

This have three type

1.      By squire :- for low undulating area

2.      By cross section: for road cannel, railway e t c

3.      By tachometric: for high undulating area.

 

 

Uses of contour

·       Drawing of the section

·       Selection and location  of  road

·       Determination of inter-visibility between two points.

·       Measurement of catchment area.

·       Calculation of reservoir capacity.

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