Reading Topographic Maps and Calculating Map Scale

This page was developed by Leslie Kanat from Johnson State College.
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Students will use a topographic map and define the watershed drained by Joe Brook, draw a bar scale, and calculate a ratio scale.

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Learning Goals

Students will be able to:
  • apply quantitative skills to solve map scale problems
  • discover the meaning of a watershed

Context for Use

This homework assignment is appropriate for an introductory level, general earth science course that requires an understanding of map scales. Students will need prior experience working with bar scales and map scales, and have a cursory understanding of the meaning of a watershed. The activity can generally be completed within one hour.

Description and Teaching Materials

The instructor should work with a variety of topographic maps prior to assigning this activity. Only one .pdf file is needed for this assignment.

Assignment handout (Acrobat (PDF) bytes Jun25 06)

Teaching Notes and Tips

Instructors should demonstrate how a map bar scale can be used to calculate a ratio scale and how a ratio scale can be used to draw a bar scale. Examples should use a variety of map scales; the mathematics, and proper use of cancelling units, should be demonstrated a priori.


Instructor should carefully trace the proper watershed on each assignment and make careful notes about the quantitative reasoning skills applied by the student. Once the assignment is returned, the instructor should present the correct format in front of the entire class.

References and Resources

General introduction to topographic maps:

Ratio scales defined by the Geology Department at Idaho State University: