She’ll be coming around the mountain, but what will her road look like? Take a real or invented mountain, model it out of clay, and discover how we can represent it using topography. So what is topography, anyway? It's a field of earth science that involves studying and modeling the surface shapes and features of the earth (and even other planets!). Whether you have a picture of a mountain in your mind or you have a mountain of your own you’d like to create, this hands-on experiment will help you understand the tough work of a cartographer.
Cartographers make, read, and learn from maps. You may have seen maps that look like a lot of squiggly lines on paper. These are topographic maps. Sometimes the lines are wiggly; sometimes they are straight. They may be very close together or far apart. These lines represent the three-dimensional landscape drawn in two dimensions. Elevation, or the height of a landform, can be tough to show in two dimensions. The steepness, also known as the slope, can be hard to demonstrate as well—but it’s possible!
To make a 3-D landscape on a flat piece of paper, mapmakers draw lines called contours. These lines represent points that are all equal in elevation, or height. The contour interval, or the space between lines, tells you how much of an elevation change there is between those two places. When the lines on a topographic map are far apart, the land in between them has a gentle slope, and when they are close together, the land has a steep slope.
There are other ways of representing a 3D reality on a 2D map as well. If you’ve looked at older maps, you may also see hachures. These are short line segments or curves drawn in the direction of a steep slope.
Create a three-dimensional topographic model of a mountain. Use this to create a two-dimensional topographic map.
- Dental floss
- 8 ½ x 11 piece of white card stock
- Permanent marker
- In this experiment, you’ll figure out how contour lines work. First, build your mountain.
- Take a handful of soft, air-drying clay and make a mountain out of the clay. Make sure that you have lots of interesting and realistic landscape features, such as river valleys and craggy peaks.
- Now, move your clay mountain to a piece of white card stock.
- Stand a ruler vertically next to your mountain by pressing it into a small lump of clay.
- Use your toothpick to make four small, evenly spaced marks at different points about ½ an inch above the paper.
- Make a new set of marks ½ an inch above that, and so on, until you get to the top of your mountain. For this model, ½ inch will act as your contour interval.
- Use your permanent marker to draw around the base of your mountain. This indicates the spot on your mountain where the elevation is at sea level.
- Get your dental floss ready. Stretch out a piece that’s at least double the width of your mountain at its widest point.
- Now, cut straight across the clay, slicing through the first four half-inch contour marks.
- Remove the bottom part of the clay mountain, and place the new, shorter mountain on the paper. Make sure not to rotate this segment!
- Draw around the bottom of the clay again. This is what your mountain looks like at the ½ inch contour interval.
- Keep on moving up the mountain with your dental floss, making a cut at each contour interval. At each interval, use your permanent marker to make another outline around the new base of the mountain. Continue until you have no more contour intervals left.
- Remove the clay from the paper. Now you have a topographic map!
Can you see where your mountain was steep and where it was flat? How can you do this?
Place an 8 ½ x 11 piece of card stock on the ground. Draw a pathway lengthwise on the piece of paper. Now, lift one end of the paper half an inch off the ground. That paper takes 11 whole inches to rise half an inch! It is pretty flat. If you were walking up that pathway you drew, you might be a little out of breath, but it would not be too difficult.
Now, place the same piece of paper on end and tilt it very slightly. This piece of paper rises almost vertically over a very short distance. Look at your pathway now. It goes almost straight up! You would need mountain-climbing equipment to climb up this path. Your paper rises 11 inches in elevation, but covers only half an inch of horizontal distance—the slope is almost vertical.
When you created your topographic map, the lines on your paper reflect what your clay mountain looked like. If the rise were sudden and steep, the lines would be close together. If the rise were slow, the lines would be farther apart. This way, we can use topographic maps to tell whether a hike might involve a tough climb or an easy walk.
Take a look at a real topographic map and see if you can find places where the slope is steep and where it is flat!