What is contour interval?/ Uses of contour maps in surveying.

Let us go through some of the FAQs related to contour lines.

1. What is contour interval?

 A Contour interval is the elevation difference between the successive contour lines represented in a topographical map.

For eg: Suppose a contour map has a contour line of 80, 85, 90, 95, & so on, 

Then the contour interval  = [85 -80] 

                                          = 5 units.

2. What are the factors that affect the selection of contour intervals?

The contour interval depends upon the following factors.

1. Nature of ground surface:

Plain ground: The contour intervals are generally small & are parallel.

Steep slope: The contour intervals are generally big & are unequal 

2. Scale of the map:

The contour spacing will be large for a map having a small scale. For the larger scale map, the contour intervals are made of less spacing.

3. Purpose: 

For the precise & detailed survey work, the contour interval should be smaller. For the rough survey work such as location survey, finding catchment area, finding the capacity of water bodies, etc. we need larger contour intervals.

3. What are the uses of contour maps in surveying?

1. Contour map provides the topography of the ground.

2. Helps to select the location of infrastructures such as dams, bridges, pipelines, roads, etc.

3. We can determine the area & volume of the earth of a particular locality.

4. We can calculate the area & capacity of a reservoir or any water bodies.

5. The contour gradient can be drawn from the map.

6. We can find the difference in the height of any two points.

7. To find the economical route of communication between two places.

8. To ascertain the profile of the ground surface in any direction.

4. What are the different types of contour lines?

There are 3 types of contour lines on a map. They are

a. Index lines:

Index contour lines are shown as the dark & thick lines in the maps. These lines provide us the elevation data with respect to the sea level. Usually, one index line is shown after every five intermediate lines.

b. Intermediate lines:

These are the more common lines drawn in between the two index lines. They are thin lines when compared to the index lines.

c. Supplementary lines:

These are the dotted lines, indicating flatter terrain.

To understand A to Z of surveying, click here.

Thank you for going through this article❤. Have a good day 😄.

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