Topographic maps are made specifically to show elevation. They show elevation through the use of contour lines.

*The mountain below has 1 peak! 4000m

What is the lowest elevation of this mountain?  1000 m

PLEASE NOTE: Not every elevation can be represented by a contour line.

Index contours: bold contour (lines used to calculate the contour)

Interval: the distance between the contour lines

* How do you figure out the contour interval on a topographic map?

  • take 2 index contours near each other  (On this map: 800’ and 700’)

  • find their difference/subtract (800’-700’ = 100’)
  • count the # of lines from one index contour to the next  (On this map: there are 5 contour lines from 700’ to 800’ (4 in between them and the final line of 700; 4+1= 5 lines)
  • divide the difference in elevation by the # of lines!  (100’ divided by 5 lines = 20’)

Contour lines are a type of isoline: (“iso-“ means equal): all places along the same contour line have the same elevation! No matter where you stand on the 100’ contour line, the elevation will always be 100’, whether you’re on the N, S, E, or W side of the mountain. You can tell how steep the mountain is by how close together the contour lines are to one another!  The closer the lines = the steeper A local depression (like a the mtn.!volcanic crater or a dried-up lake bed) can be shown on a topographic map by drawing hachures: short lines that point from a contour line toward lower elevations.

What is the contour interval of this figure below? 25ft

The steepness of the terrain is also known as the gradient:  the change in elevation for a given horizontal distance. You can calculate the gradient of an area using the following:

  • If you travel 10 miles on a straight road, and your…Topographic maps show you a birds-eye view of an area (looking down on the landscape).
  • If you want to know what the mountain looks like from the side, then you draw a profile: a side-view of the landscape
  • A profile shows how the elevation changes along a straight line between two points.


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Andy Wong
Andy Wong
12 years ago

Sorry, about that! The article has been updated with new content and the correction! Thanks Shawn!

12 years ago

You did it wrong. The contour interval is 20m.