Contour Lines

Features like mountains, plateaus, valleys, waterfalls, seas, lakes, etc. are known as the Relief of the Land. A relief map represents these reliefs. Contouring is the standard method for representing the relief on a map.

The surface of the Earth is obviously not uniform. It has mountains, hills, plateaus, valleys, waterfalls, seas lakes, etc., representing the elevation and the depression on the Earth�s surface.

So how do we represent contour lines through a 3-D model?

These models are difficult to make and handle and are comparatively expensive. A relief map basically shows the height of the land above the mean sea level on a flat surface.

Several methods have been developed to depict the relief features on a map like contouring, form lines, spot height, benchmarks, hachures, etc. But the standard method is Contouring. And that is where Contours come into play.

What are Contour Lines?

Contour is actually an imaginary line, which joins the points or places having the same height above the mean sea level. So it is actually a line of constant height above the mean sea level. Are these lines drawn just on the basis of assumption? No, they are actually drawn by surveys done in the field.

Let us see some definitions:

Contour interval or Vertical contour refers to the difference between the value of any two successive contours.

Do you know how they look on a map?

They are usually constant on a map. Similarly, the horizontal difference between the values of any two contours is called Horizontal Equivalent. This depends upon the slope of the Land.

Characteristics of Contour lines

Contourlines can never cross each other. If they cross, that would mean that they are at the same location, which is obviously not possible. This is their basic characteristic. Also when two contour lines having different heights meet, it means that the slope is vertical like a cliff or a waterfall. The spacing between the contour lines indicates the nature of the slope. Can you guess what widely spaced contour lines indicate? They indicate gentle slopes. The closely spaces contours indicate steep slopes.

All contour lines are marked with a number, which indicates their height above the mean sea level in meters or in feet. The contour with zero value represents the coastline because they are exactly at sea level.

Contour Lines Questions

1. Which of the following is not used to depict relief features of any place?
(i) Contouring
(ii) Spot height
(iii) Benchmarks
(iv) Maps

2. Which of the following is represented by the spacing between the contour lines?
(i) Vertical Slope
(ii) Steep Slope
(iii) Height above Sea Level
(iv) Nature of the Slope

What does the contour value with 0 indicate?
(i) Highest Point of Mountain
(ii) Any Plain Surface
(iii) The Deepest Point in the Ocean
(iv) Coastlines

3. Which of these will have two contour lines of different heights?
(i) Mountain
(ii) Coastline
(iii) River
(iv) Cliff

4. The difference between the values of any two successive contours is called _____.
(i) Horizontal equivalent
(ii) Successively Equivalent
(iii) Spot Height
(iv) Vertical contour

Read More: Representation of Relief Features By Contours: Features Of Contour Lines