![]() Contour cross a water shead or ridge line at right angles. A closed contour line with one or more higher one inside represents a hill similarly contour line with lower value inside indicates a depression or pond. A single contour line cannot split into two contour line. A contour line must close upon itself through not necessarily within the limits of the map.į. If the contour line are spaced closer and non-uniform then it shows steep and undulated ground.Į. If the contour lines are parallel and distance apart then it shows that the ground is gentle slope.ĭ. Contour overlap or unit in a single line in case of vertical cliff.Ĭ. Two contour lines donot cross each other except in the case of overhanging cliff.ī. The horizontal distance between two points on two consecutive contour lines for a given slope is called the horizontal equivalent. So, if the available time and cost is limited larger contour interval is used. If the contour interval is small greater time and cost is required in survey and map plotting. But in case of location surveys where the desired accuracy is less, higher contour interval should be used. Surveying for detailed design work or for earthwork calculations need high accuracy so small contour interval is used. if the scale of map is large, the contour interval is considered to be small and vice versa.Īccuracy needed in survey work also decides the contours interval. The contour interval normally varies inversely to the scale of the map i.e. For flat ground, a small contour interval is choosen, whereas for undulating ground, higher contour interval is chosen. The contour interval depends upon the nature of the ground. The choice of a suitable contour interval in a map depends upon four principle considerations. This vertical distance between any two contour lines in a map is called the Contour Interval ( CI) of the map. The difference in elevation between successive contour lines on a given map is fixed. ![]() ![]() Figure: Elevation of nearby contour line. A contour line marked by a heavier line weight to distinguish it from intermediate contour lines is called index contour line.Īn index contour line shows the elevation of nearby contour line. The method of plotting contours in a plan or map is called conturing.It helps to visualize the relief of ground in two dimensional plane or map.A line joining points of equal elevations is called a contour line.From the contours, it is possible to determine the capacity of a reservoir. This study is very important in locating bunds, dams and also to find out flood levels.Ħ. Catchment area and hence quantity of water flow at any point of nalla or river can be found. The routes of the railway, road, canal or sewer lines can be decided so as to minimize and balance earthworks.ĥ. Intervisibility of any two points can be found by drawing profile of the ground along that line.Ĥ. It helps in finding out depth of cutting and filling, if formation level of road/railway is decided.ģ. By drawing the section in the plan, it is possible to find out profile of the ground along that line. Suitable site for the project works to be taken up.Ģ. A civil engineer studies the contours and finds out the nature of the ground to identify. 17.5).Ĭontour maps are extremely useful for various engineering works:ġ. If contour lines cross each other, it shows existence of overhanging cliffs or a cave (Fig. If contour lines are meeting in some portion, it shows existence of a vertical cliff (Fig. Contour lines generally do not meet or intersect each other.ġ1. Contour lines with V-shaped with convexity towards higher ground indicate valley (Fig. Contour lines with U-shape with convexity towards lower ground indicate ridge (Fig. Approximately concentric closed contours with increasing values towards centre indicate hills.Ĩ. Approximately concentric closed contours with decreasing values towards centre (Fig. ![]() Irregular contours indicate uneven surface.Ħ. ![]() Equally spaced contour indicates uniform slope.ĥ. Closely spaced contour indicates steep ground.Ĥ. Widely spaced contour indicates flat surface.ģ. Contour lines must close, not necessarily in the limits of the plan.Ģ. The contours have the following characteristics:ġ. On contour lines the level of lines is also written. 17.1 shows contours in an area with contour interval of 1 m. The contour lines in an area are drawn keeping difference in elevation of between two consecutive lines constant. Such lines are drawn on the plan of an area after establishing reduced levels of several points in the area. A contour line is a imaginary line which connects points of equal elevation. ![]()
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