GEOL/METR 309: Investigating Land, Sea and Air Interactions Fall 2005, SFSU Hands-on Jig-Saw Activity: Topographic Contour Maps Dr. Dave Dempsey Dr. Lisa White (Dept. of Geosciences)

(Tuesday, Sept. 6, 2005)

Objectives:

• Learn to understand and interpret topographic contour maps of the earth's surface generally.
• More specifically, learn to recognize several topographic features by their distinctive contour patterns on a topographic map.
• Practice the jigsaw cooperative learning strategy.

Some Definitions:

• topography: the shape of the earth's surface, including features such as hills, valleys, ridges, cliffs, etc.
• map: a scaled, symbolic representation of something, such as features of the earth's surface.
• contour line: a line along which some quantity, such as elevation of the earth's surface above sea level, is constant.
• topographic contour map: a map showing the shape of the earth's surface using contour lines.

Background. Topographic maps show the shape of the earth's surface and features on it. They are extremely common and valuable tools used not only by earth scientists but by many others for a wide variety of purposes. On a topographic contour map, contour lines are lines of constant elevation, where sea level is always used as a base or reference (or "datum"), representing zero elevation. In this activity, you will build models of simple landscapes and locate contour lines on them to see how the shapes and spacing of contour lines can portray the shape of the earth's surface, such as hills, valleys, ridges, cliffs, and other topographic features.

Pedagogical Strategy: A hands-on, jigsaw approach to help students visualize how contour lines represent topography on a map. Each student first becomes an "expert" on maps of one particular landscape, then teaches other students about it.

1. In a small group, students build a model of a simple landscape with clay. (Each group in class constructs one of four different landscapes.)
2. Students physically attach string to the clay models at a series of regularly spaced elevations.
3. Students transfer the resulting pattern of string-contour lines onto an overhead transparency, creating a contour map of their landscape.
4. Each student shows members of the other groups how the contour map represents the modeled landscape.

Materials Needed:

• Clay (enough to build a model landscape 10 cm wide, 20 cm long, and up to 7 cm high at its peak, starting small and adding more clay as needed).
• String (one meter's worth should be enough for each model)
• Scissors (one per group to cut string to needed lengths)
• Plastic containers with lid (traditionally these containers have a volcano model that will be set aside for this activity)
• Clear plastic wrap (a strip about a foot wide and a foot long should be enough, on which to build the model)
• Old newspaper (to protect the table top from the gooey clay)
• Ruler with centimeter marks (one per group)
• Drawing tools (pencil, paper, eraser, and five different colors of washable marker for drawing on transparencies)
• Clear overhead transparencies (two per group; one for practice, one for final drawing)
• Tape (one per group)

Detailed Instructions:

1. An instructor will show you an example of the the kind of contour map that you'll be drawing, using a simple hill to illustrate. In your permanent group, each person should then select one of the following, slightly more varied topographic landscapes:

1. a hill with one side much steeper (nearly a cliff) than the other sides
2. a hill with two ridges extending down along its slopes with a valley in between
3. two hills, with a dip or saddle between them about half as high as the lowest hill
4. a hill next to a depression

2. The person who chooses landscape (a) above will then join their counterparts from two or three other permanent groups to form a temporary group. Those who chose landscapes (b), (c), and (d) will do the same, resulting in a set of temporary groups that we'll call "landscape groups". Introduce yourself to your landscape group members, then check to make sure your group has got everything on the list of materials above.

3. Construct a clay model of your chosen landscape, as follows:

1. Lay down some old newspaper to protect the table top. On this newspaper trace the outline of the lid of the plastic container with a pen. Cover the trace with a strip of clear pastic wrap. Build your model on the plastic wrap. Keep the base of your model within a 10 cm by 20 cm center portion of the wrap (a shape similar to the plastic container), about one inch away from the edges of the outline that you drew. (This helps ensure that you'll have room to cover the clay model with the plastic container.) Make the highest point of your model at least 5 cm but no more than 7 cm above its base.

2. Use your ruler to measure and mark lots of places on the model where the elevation is 1 cm above its base. Attach string to the clay to connect these 1 cm elevation marks. (The string should attach well to the clay and stay in place. If necessary, use a little water to moisten the clay.) At this point check with your instructors to see if you have created the 1 cm contour elevation correctly. Does the string connect to itself to form a closed loop? Did you find that you had to form more than one closed loop?

3. Repeat the previous step for elevations of 2, 3, 4, and 5 cm.(Add more as needed if your model is higher than 6 cm. You don't want your landscape to be higher than the top of the plastic box, though!)

4. Carefully lift the model and place it on the lid of the plastic container. Cover it with the plastic container itself, inverted.

5. Place a transparency across the top (bottom?) of the container and tape it in place. Now, looking straight down on the model from above, draw on the transparency each contour line as you see it below. (You're drawing projections of the contour lines onto the transparency.) Use a different color for each contour line, and label each contour line with the appropriate elevation.(Each member of your landscape group should draw at least one contour line.)

6. Sketch the contour projections for each model on separate sheets of paper for your reference, and note the key features of the contour lines (shapes, spacing) that portray the various aspects of your particular landscape.

7. There is a way to check the accuracy of the positions of your contour lines, though we won't do it here. The first step would be to move the clay model from the lid and set it into the bottom of the plastic container. Then, pour water into the container to a depth of exactly 1 cm. The water surface should be flush against the string representing the 1cm contour line, because the water surface is at constant elevation, just as the string is supposed to be at a constant elevation. More water would then be added, to depths of 2, 3, 4, and 5 cm (and more if needed) to check the other contour lines. (It may be necessary to do this quickly, as the strings may begin to separate from the model!)

4. Bid adieu to your temporary group and rejoin your permanent group. You are now the "expert" on drawing and interpreting a contour map of your particular landscape, and you will need to be able to communicate what you've learned to the others in your group. You will all responsible for recognizing the features of each landscape on a topographic contour map.

When your turn comes:
1. take your group to visit your model;
2. show the contour map that your landscape group drew; and
3. identify for your group members the features of the contour lines that portray the various aspects of your model landscape.

References:

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