Contour line basics

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Contour line is a tool widely used in many diciplines include weather map, market survey, historical analysis and, of course, earth and environmental sciences. As a consequence, to know the property of contour line is necessary for every modern citizen and should almost be a common sense to a college student. The second part of our map basics exercise is to introduce the property of contour line and its application on the topographic map. Later on, we will use this basic knowledge to examine various landscapes on map.

First, get a feeling of using contour line on a map which is trying to show the elevation of landscape. Please read the booklet "Stereogram Book of Contours" with the aid of a stereo scope. The use of stereo scope is illustrated on page 7. If you have trouble to see the 3D vision of the contour lines, call instructor for help.

Second, read this this link for a nice introduction to the use of contour line.

Let's see some basic definitions:

  • What is a contour line?
    • On a topographic map, contour line is used to show
  • The origin of contour line
    • A contour line may look crooked and distorted on a map, but every contour line is absolutely (vertical, horizontal or tilted)
  • The contour interval
    • Every topographic may have (only one, more than one) contour interval.
    • The contour interval on a normal 1:24,000 USGS Quadrangle map is ft.
    • On an example of 1:24,000 map below, the difference of elevation between locality A and locality B is approximately feet. (hint: it is more convenient to count the thick (index) contour line instead of the thin contour line. How much difference in elevation between two adjacent thick contour lines? )
  • In the map above, the horizonal ground distance between locality A and locality B is: (hint, the distance on map is 2 inches. And, what is the scale of this map?) Would a different contour interval affect the horizontal distance? (yes, no)
  • The (larger, smaller) the contour interval, the more detail of landscape could be show.

Rules of using contour line

Contour line can not be randomly drawn. There are a set of rules must be followed strictly. Please read a web page for the explanation of the rules.

Based on the rules of using contour line, please consider the following questions:
The right side map (map 1) shows four contour lines, if the contour interval is 20 feet, how many contour lines can be added between adjacent two existed lines? Ans:

Under a normal situation, the elevation of location A is not known, but it could be in between and .

If the highest elevation shown in this simple map is only 375 ft. then the contour line close to location A should have a value of . (review one of the rule)
Map drawing 1
In the right side map drawing (map 2), which location (A or B or C) has higher elevation. (review rule).
Ans:

If the contour interval is 60 ft, then the elevation difference between locality A and locality B is

Map drawing 2

In the map drawing on the right (map 3), it could represent a landscape with (choose all the possibilities)

three vallies (click to cancel )

three ridges (click to cancel )

one valley and two ridges (click to cancel )

two vallies and one ridge (click to cancel )
Map drawing 3

The right side map drawing (map 4) shows a volcano with a central crater and a small side crater.The contour line interval of this map is 100 ft.

The elevation of this volcano does not exceed feet. (review rule)

The depth of the central crater is not deeper than feet.

Elevation at the bottom of the small crater B should be higher than ft.

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    Map drawing 4