Answer key: Reading a Contour Map Activity

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Goal: Read a topographic map: find the contour interval, read elevations, compare slopes, use the V-rule to find which way a river flows, and sketch a cross-section.

Supports map-reading skills used in MS-ESS2-2 investigations (how geoscience processes shape Earth’s surface).

Completed results table

Read from the 20 m contour lines. For a point between two lines, any estimate between them is fine.

Contour interval: 20 m. Index lines are labeled every 100 m, with 4 thin lines between them.

The map and the X–Y cross-section

Answers

1. How can you work out the contour interval from the labeled (index) lines?

   Neighbouring index lines are 100 m apart (for example 300 and 400) with 4 thin lines between them, so 100 m is split into 5 equal steps: 100 ÷ 5 = 20 m.

2. Point B is between two lines. Explain how you estimated its elevation.

   B lies about halfway between the 420 m and 440 m lines, so it is about 430 m. Any estimate between the two lines is reasonable; halfway is the best guess.

3. Which side of the valley is steeper: north of the river or south of it? How can you tell from the map?

   North. The lines are packed close together there. Along X–Y the ground drops about 224 m in 1.3 km north of the river, but rises only about 150 m in 1.8 km south of it.

4. Which way does the river flow? Use the shape of the contour lines where they cross it.

   West, toward the left edge. Where the lines cross the river they bend into Vs that point east, upstream; water flows the other way, downhill. The river is about 290 m at C but below the 160 m line where it leaves the map in the west.

5. Sketch the cross-section from X to Y: mark where X–Y crosses each thick line, then join the points smoothly.

   The ground falls steeply from about 539 m at X to the river at about 315 m, 1.3 km from X, then climbs gently to about 465 m at Y.

6. Along X–Y, how much higher is the highest point than the lowest point?

   The highest point is near X, about 539 m; the lowest is the river, about 315 m. The difference is about 224 m.