What is contour :-
It is an imaginary line on he ground , joining the points of some elevation or some R.L is called as contour.
Contour
What is contour line :-
A line passing through point of equal elevation or equal R.L is called as contour line
* A contour line is a line on the map represent on the contour .
* In a topographic map , the relative altitude of the ponts can be represent by contour line .
* By means of contour line , the nature of the ground sloping , steep slope , and ground slope , hills and valley can be shown in the topographic map
What is contour interval :-
The vertical distance between any two consecutive contour is known as contour interval .
* It is the vertical distance between two successive contour .
* It remains constant for a given map .
* The difference in R.l of two contour gives contour interval .
Choice of contour interval :-
* Nature of ground :- For a flat ground a small interval is necessary . if the ground undulating or sloping the counter interval will be large .
* Scale of the map :- If the scale of the map is mall, the contour interval should large .
* Propose and extent of the survey. if the survey is done for detailed designed or for accurate earth work calculation small contour interval used.
* Horizontal equivalent :- The horizontal distance between two points consecutive contour is known as horizontal equivalent .
* Horizontal equivalent depends upon steepness of ground.
Characteristics of contour:-
* The two contour line of different elevation cannot cross each other . Except in case of overhanging cliff.
* contour line close together indicate steep slope
* If they are far apart threy indicate gentle slope .
*If they equally spaced then in indicate uniform slope .
*A serise of straight , parallel equally spaced contours represent a plane surface .
* A series of contour line with higher value inside indicate a hill .
* A series of contour line with lower value inside the loop always indicate depression or valley.
*Contour line cross a ridge line or watershed line at right angle and form (U) shaped contour .
* contour line cross a valley line at right angle and form ( v ) shaped contour
* nAll points on a contour line hve equall elevation .
Methods of locating contour :-
1. Direct method :-
* By spot level .
* By radial line .
2 Indirect method :-
* Square method.
* method of cross section .
* Tacheometric method .
* Plane table method .
Direct method:-here the contour to be plotted actually traced on the ground by locating the points of that elevation .
Indirect method :- Here the spot level are taken at some selected points caused as guide points and the level of the points are determine . The contour are then drawn from the interplotation from the level of the guide points .
Uses of contour map:-
* to drow longitudinal section and plan of the given map.
* To determine nature of ground in prepaired area.
* To calculate reservoir capacity .
* To measurement of drainage area .
* To determine inter visibility between two points .
* To find intersection of surface and measurement of earth work.
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