Contour

What is contour? explain contour interval, necessity of contour plotting??

Contour:- A contour is an imaginary line on the ground joining the points of equal elevation. It is a line in which the surface of ground is intersected by the level surface. a contour line is a line on the map representing a contour.

Contour Interval:

The vertical distance between any two consecutive contours is called contour interval. The contour interval is kept constant for a contour plan, otherwise the general appearance of the map will be misleading. The horizontal distance between two points on two consecutive contours is known as the horizontal equivalents and depends upon the steepness of the ground. the choice of proper contour interval depends upon the following consideration.

(i) The nature of the ground: The contour interval depends upon whether the country is flat or highly undulated. A contour interval choosen for a flat ground will be highly unsuitable for undulated ground. For every flat ground, a small interval is necessary.

(ii) The scale of the map: The contour interval should be inversely proportional to the scale. If the scale is small, the contour interval should be large. If the scale is large, the contour interval should be small.

(iii) The purpose and extent of the survey: The contour interval largely depends upon the purpose and the extent of the survey. For example, if the survey is intended for detailed design work or for accurate earth work calculations, small contour interval is to be used. The extent of survey in such cases will generally be small. In case of location surveys, for lines of communications and for reservoir and drainage areas, where the extent of survey is large, a large contour interval is to be used.

(iv) Time and expense of field and office work: If the time available is less, greater contour interval should be used. If the contour interval is small, greater time will be taken in the field survey, and in plotting the map.