Title: Water and Land 207

Key Words: map projections, equal area, Mercator, polar, Robinson, Van der Grintem

National Standard: 1 (Using maps and other geographic representations)

State Standard: 10 (Using maps and other geographic representations)

Teaching Level: Middle School

Introduction: About 70% of the earth's surface today is water, and just 30% is land. These proportions were quite different just 25,000 years ago. We live today during a warm spell in Earth's history; so much ice has melted and ocean levels are fairly high. But during cold periods, ocean water is taken up into ice and permanent snow, sea level drops, and long submerged land reappears. The next time this happens, probably not very long from now, the coast line of the eastern United States will shift steadily eastward as much as 150 miles. The US Coastal Plain will nearly double in size, and cities such as Jacksonville, Florida, Charleston, South Carolina, and Baltimore, Maryland will lay many miles from the sea. People will be able to drive from England to France without using the Channel Tunnel.
Any map of North America (or of any other continent), therefore, is a still picture of a changing relationship between land and water.

Objective: Students will examine maps of different projections, mathematically calculate distortions, and note the advantages and disadvantages of each map.

Materials: World maps of different projections, graph paper, chart paper.

Procedure: Collect world maps of different projections (Equal area, polar, Van der Grinnten, Robinson, Mercator).

Transfer the map onto the graph paper (continents and oceans).

Using the graph paper grid, calculate the amount of land and water represented on each of the projections.

Compare the distortions of the projections, based on the 30% land, 70% water relationship suggested by Harm de Blij. Make a chart of these comparisons.

Discuss the advantages and disadvantages of each type of projection (the advantage of Mercator is reading latitude and longitude; the disadvantage is the distortion of land areas).

The Mercator Projection was designed for marine navigation, a straight line between points crosses meridians at the same angle.

Draw conclusions: Maps have advantages and disadvantages as tool for different tasks.

Evaluation/Assessment:
Label the same two cities on two different map projections. Have students calculate the distance between the two cities. Explain the difference in the distance measurement.

Extension/Enrichment: Students begin with a piece of rectangular paper representing the earth.
For mathematical ease, paper should be one of the following sizes. More discussion will be generated if all these sizes are used throughout the class.

18" x 20"
24" x 15"
12" x 15"
10" x 18"
5" x 12"
9" x 10"

Based on the 30% land and 70% water distribution figures used above, have students calculate how much area of this "earth" should be covered by land. Have each student cut a piece of contrasting colored paper to represent 30% of his "earth." From this contrasting paper, students will tear the shapes of the continents being sure to use all the paper, and place them in relative positions on the earth. Discuss this process.

Reflection: How successful was this lesson? Did all students benefit? Were there any surprises? What might you do differently another time? Please note any changes that will make this lesson more effective and useful in the future and pass them along to the NHGA. We appreciate your comments.
Thank you,
The authors


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