Contour Map Playground
Shape a landscape and watch its topographic map draw itself alongside. Raise hills, carve valleys, flood the land with the sea, and slice a cross-section to see the shape the lines describe.
Landscape
Topographic map
Contour interval 20 mPoint at either view to read the elevation and slope.
Cross-section A–B
A to B is 4.9 km long. The highest point is 482 m, 2.5 km from A; the lowest is 173 m, at B. Heights are stretched ×2.9 (vertical exaggeration) so the shape is easy to see.
How to read contour lines
A topographic map shows the height of the land with contour lines. Each line joins places at the same elevation, so the pattern of lines shows the shape of hills, valleys and cliffs on a flat sheet of paper.
- Elevation. A contour line’s number is its height above sea level, in meters. Every point on the line is at exactly that height. The coastline is the 0 m contour.
- Contour interval. The height difference between one line and the next is the contour interval. On one map it never changes: 10 m, 20 m or 50 m in this playground.
- Index lines. Every fifth line is thicker and labeled. Count the steps between two labels to find the interval: 100 m apart with four thin lines between them means 100 ÷ 5 = 20 m.
- Steep or gentle. Lines close together mean steep ground; lines far apart mean gentle ground. A cliff squeezes many lines into a tiny space.
- Closed loops. A set of loops, one inside another, is a hill. The smallest loop in the middle is the hilltop.
- Depressions. A loop with small ticks (hachures) pointing inward is a hollow, lower than the line around it, like a volcano’s crater.
- The V-rule. Where lines cross a river they bend into a V. The V points upstream, so the river flows the other way.
- Ridges and valleys. Lines bend into U or V shapes in both. If the point of the bend aims toward lower numbers (downhill), it is a ridge; if it aims toward higher numbers (uphill), it is a valley.
Worked example
This is the Single hill, the landscape the playground opens with, drawn with a 20 m contour interval.
1. Find the contour interval
Two neighboring index lines are labeled 300 and 400: they are 100 m apart. Between them are four thin lines, which split the 100 m into five equal steps. Interval = 100 ÷ 5 = 20 m.
2. Read the elevation at Q
Q lies between the 360 m and 380 m lines, a little closer to the 380 m line. A good estimate is about 375 m. The model’s exact value is 374.8 m.
3. How steep is the east side?
Due east of the summit, the 400 m line and the 300 m line are about 500 m apart on the ground (use the scale bar). The slope is rise ÷ run = 100 ÷ 500 ≈ 0.20, a 20% grade or about 11°. A road that steep would be very hard to cycle up.
Slope as rise over run is the same idea as the slope of a line in math: see slope and lines on Geometry Lab.
Common mistakes
- Reading the number of lines as the height. Count steps, then multiply by the interval: the fifth line above 200 m on a 20 m map is 300 m, not 205 m.
- Assuming the interval is 10 m. Always work it out from the index lines or the key. Maps of mountains often use 50 m or more.
- Thinking a closed loop is always a hilltop. Check for ticks: a loop with hachures is a hollow.
- Getting the V-rule backwards. The V points upstream, toward higher ground. Rivers flow away from the point of the V.
- Forgetting the vertical exaggeration. Cross-sections stretch heights so slopes are easy to see. The real hill is much flatter than the profile looks.
What this model simplifies
The landscape is a grid of 96 × 64 squares, each 62.5 m across, covering 6 km × 4 km. Heights between grid points are filled in by straight-line (bilinear) interpolation, and contour lines are traced with the marching squares method, the same idea mapping software uses. Real topographic maps come from surveys, aerial photos and laser scanning (lidar), with much finer detail, and they show roads, buildings and vegetation too. The landscapes are fictional, the river simply follows the steepest way down, and the sea is a flat level you can raise or lower.
Contour map activity
A one-page printable worksheet for grades 6–10, about 15 minutes: a printed contour map of a river valley, a table of elevations and six questions, from the contour interval to sketching a cross-section.
Share the playground with your class in one click. Students need no accounts or logins.
Share to Google ClassroomContour map questions
What is a contour line?
A contour line joins points on a map that are at the same height above sea level. If you walked along one, you would never go uphill or downhill. A map full of contour lines (a topographic map) shows the shape of the land on flat paper.
What is the contour interval?
The contour interval is the difference in height between neighboring contour lines, for example 20 m. It is usually printed in the map key. If it isn’t, find two labeled index lines, subtract their heights and divide by the number of steps between them.
How can you tell if a slope is steep on a contour map?
Look at the spacing. Lines that are close together mean the height changes quickly over a short distance: steep ground. Lines far apart mean a gentle slope. In this playground, the Steepness overlay marks slopes steeper than 15°.
What do the small ticks on a contour line mean?
Short ticks (hachures) on a closed loop mark a depression: a hollow, pit or crater that is lower than the ground around it. The ticks point downhill, into the hollow. Without them, a closed loop is a hilltop.
How do contour lines show which way a river flows?
Where contour lines cross a stream or river, they bend into a V or U shape. The point of the V always points upstream, toward higher ground. The water flows the opposite way. This is called the V-rule.
Can contour lines cross or split?
No. A point can only have one height, so two different contour lines never cross and a line never splits. They can run very close together at a cliff. Every contour line eventually closes into a loop, though on a map it may leave the edge first.
Is the Contour Map Playground free for classrooms?
Yes. It is free with no sign-up and runs in any modern browser, including school Chromebooks. There is a printable 15-minute activity and an answer key for teachers.