Saturday, February 9, 2013

Compare Maps with Different Projections Skills

Compare Maps with Different Projections

1.    Why Learn This Skill?
Throughout this book you will see many different kinds of maps. Some maps show the sizes and shapes of countries differently. You may wonder why this is so.
Over the centuries Arab, Chinese, and European mapmakers have developed different ways to show the round Earth in the form of a flat map. These different representations of the Earth are called projections. Each projection has its own name, such as Robinson Projection or Mollweide Projection.

Every map projection has distortions, or parts that are not accurate. This is because the shape of the round Earth needs to be split or stretched to make it flat. Identifying these distortions will help you understand how map projections can best be used.

2.    Map Projections and Their Uses
Different kinds of map projections have different kinds of distortions. Some map projections distort the shape or the size of the area shown. Some show distances to be greater or less than they actually are. One way that mapmakers classify map projections is by the properties that are distorted the least.

Map A is an equal-area projection. Notice that there is equal area on either side of the equator and on either side of the prime meridian. An equal-area projection shows the sizes of regions in correct relation to one another, but it distorts shapes. Because an equal-area projection shows correct size relations of regions, it is useful for comparing information about different parts of the world.

Map B is a conformal projection. A conformal projection shows directions correctly, but it distorts sizes, especially of places near the poles. On Map B the lines of longitude are all an equal distance apart. On a globe the lines of longitude get closer together as they near the poles, where they meet. Also notice on Map B that the lines of latitude closer to the poles are farther apart. On a globe the lines of latitude are an equal distance apart. The Mercator projection, shown on Map B, is just one example of a conformal projection. Map C on page 104 is an example of a Robinson projection, a combination of equal-area and conformal projections.

Map D, which appears on this page, is an equidistant projection. It shows accurate distances from a central point. Any place on Earth can be chosen as the central point. When one of the poles is the chosen central point, the map is called a polar projection. Either the North Pole or the South Pole can be the center of a polar projection. Notice on Map D that the North Pole is at the center. Map D is both a polar projection and an equidistant projection. The lines of latitude appear as circles, and the circles farther from the center are larger. Lines of longitude on Map D appear as straight lines that extend from the center in all directions like the spokes of a wheel.

3.    Understand the Process
Compare and contrast Maps A, B, C, and D by answering the questions in the next column. As you answer the questions, think about the advantages and disadvantages of each map projection.

  1. South America is much larger than Greenland. Which projection shows Greenland's size more accurately,
    Map A or Map B?
  2. The greatest east-west distance in Africa is about the same as the greatest north- south distance. Which projection shows Africa's shape more accurately,
    Map A or Map B?
  3. On which maps do the lines of longitude get closer together toward both poles?

4.    Think and Apply
Write a paragraph about the advantages and disadvantages of using each kind of map.

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