CONTOUR MAPS & THEIR
USES
USES
A contour line is a imaginary line which
connects points of equal elevation. Such lines are drawn on the plan of an area
after establishing reduced levels of several points in the area. The contour
lines in an area are drawn keeping difference in elevation of between two
consecutive lines constant. For example, Fig. 1 shows contours in an area with
contour interval of 1 m. On contour lines the level of lines is also written.
connects points of equal elevation. Such lines are drawn on the plan of an area
after establishing reduced levels of several points in the area. The contour
lines in an area are drawn keeping difference in elevation of between two
consecutive lines constant. For example, Fig. 1 shows contours in an area with
contour interval of 1 m. On contour lines the level of lines is also written.
Fig. 1: Contours
1. Characteristics of Contours
The contours have the
following characteristics:
following characteristics:
1. Contour lines must
close, not necessarily in the limits of the plan.
close, not necessarily in the limits of the plan.
2. Widely spaced
contour indicates flat surface.
contour indicates flat surface.
3. Closely spaced
contour indicates steep ground.
contour indicates steep ground.
4. Equally spaced
contour indicates uniform slope.
contour indicates uniform slope.
5. Irregular contours
indicate uneven surface.
indicate uneven surface.
6. Approximately
concentric closed contours with decreasing values towards centre (Fig. 1)
indicate a pond.
concentric closed contours with decreasing values towards centre (Fig. 1)
indicate a pond.
7. Approximately
concentric closed contours with increasing values towards centre indicate
hills.
concentric closed contours with increasing values towards centre indicate
hills.
8. Contour lines with
U-shape with convexity towards lower ground indicate ridge (Fig. 2).
U-shape with convexity towards lower ground indicate ridge (Fig. 2).
Fig. 3
9. Contour lines with
V-shaped with convexity towards higher ground indicate valley (Fig.3).
V-shaped with convexity towards higher ground indicate valley (Fig.3).
10. Contour lines
generally do not meet or intersect each other.
generally do not meet or intersect each other.
11. If contour lines
are meeting in some portion, it shows existence of a vertical cliff (Fig. 4).
are meeting in some portion, it shows existence of a vertical cliff (Fig. 4).
12.
If contour lines cross each other, it shows existence of overhanging cliffs or
a cave (Fig. 5).
If contour lines cross each other, it shows existence of overhanging cliffs or
a cave (Fig. 5).
2. Uses of Contour Maps
Contour maps are
extremely useful for various engineering works:
extremely useful for various engineering works:
1. A civil engineer studies the contours and finds out the nature
of the ground to identify. Suitable site for the project works to be taken up.
of the ground to identify. Suitable site for the project works to be taken up.
2. By drawing the section in the plan, it is possible to find out
profile of the ground along that line. It helps in finding out depth of cutting
and filling, if formation level of road/railway is decided.
profile of the ground along that line. It helps in finding out depth of cutting
and filling, if formation level of road/railway is decided.
3. Intervisibility of any two points can be found by drawing
profile of the ground along that line.
profile of the ground along that line.
4. The routes of the railway, road, canal or sewer lines can be
decided so as to minimize and balance earthworks.
decided so as to minimize and balance earthworks.
5. Catchment area and hence quantity of water flow at any point of
nalla or river can be found. This study is very important in locating bunds,
dams and also to find out flood levels.
nalla or river can be found. This study is very important in locating bunds,
dams and also to find out flood levels.
6. From the contours, it is possible to determine the capacity of a
reservoir.
reservoir.
google-site-verification=2j8Us0psP3GGjD12h0fH6_Z08_sRyWQjNbWcaMV4E9A