Isolines on maps connect points of equal value. It might be isotherms joining points of equal annual temperature on a climate map, isobars on a weather map joining points of equal barometric pressure, isopleths on a population map joining points of equal density, or isohyets joining points of equal precipitation. Our purpose here is to visualize the lines joining points of equal elevation- contour lines- most often associated with a topographic map.
A map’s point of view is vertical: the reader is theoretically looking down although, of course, you can read it from any angle you like. Visualizing what a contour pattern actually looks like from ground level is another story. As Compass Dude puts it, “when you follow a path on a topographic map that crosses these contour lines, you will be either climbing or descending; a path running parallel to contour lines is relatively flat.” It adds: “when reading a topographic map, you need to visualize in your mind's eye a 3-dimensional view of what the symbols and contour lines are representing.”
Basics of Contour Lines:
With all isolines, the pattern can be viewed and perhaps better understood in the form of a block diagram: it is even useful, at times, to construct a profile (see images). Sometimes shaded relief (dark and light shaded slopes) is used to help in visualization. But in simple terms: the closer the spacing the steeper the slope.
Some landform features are easily recognizable. For instance:
- a circle- a hill top
- lines pointing sharply towards a hilltop- a valley
- lines pointing widely away from a hilltop- a ridge
- long row of lines closely spaced- a cliff
Test your ability to associate contour lines with the block diagram versions of patterns adapted from the Journal of Geography, then check the answers below (see image).
Construction of Models:
One way to help in the understanding of contour lines is to construct a model. Following is a suggested exercise.
To make a three dimensional cardboard model of the relief of an area using a contour or topographic map:
- On a sheet of paper trace the major contour lines from the lowest to the highest. Do this for every level.
- Using a separate sheet of cardboard for each contour level from the base to the top, trace and then cut away levels as you go. Fasten the sheets together with glue.
As an added exercise you could:
- Layer tint the model layers
- Attempt to identify the types of landform features
Answers to Match Questions:
- 1st block diagram represented by #7 contour pattern
- no sample contour pattern for 2nd block diagram
- 3rd block diagram represented by #2 contour pattern
- 4th block diagram represented by #6 contour pattern
- 5th block diagram represented by #3 contour pattern
- 6th block diagram represented by #8 contour pattern
- repeated- 7th block diagram represented by #2 contour pattern
- 8th block diagram represented by #1 contour pattern
Sources:
- Journal of Geography. March/April, 1988
- Topographic Maps. Compass Dude.
James Gibson - James Gibson is a retired teacher and small business owner. He is a published writer and has a wide spectrum of interests.
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