CHAPTER 2 SECTION 2 Mapping the Earth’s Surface - Erie City School ...

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CHAPTER 2 Maps as Models of the Earth

SECTION

2

Mapping the Earth's Surface

BEFORE YOU READ

After you read this section, you should be able to answer these questions:

? What is a map projection? ? What are four types of map projections? ? What information should every map have? ? What are four tools used by modern mapmakers?

What Happens When a Globe Becomes a Map?

Because a globe is a sphere, a globe is the most accurate model of Earth. However, a globe is too small to show many details of the Earth's surface, such as roads and rivers. In order to show these details, we use maps.

A map is a flat model of Earth's curved surface. Maps can show many details that globes cannot. However, moving information from a curved to a flat surface causes errors in shapes, sizes, and distances. These errors are called distortions.

Below is a picture of an orange. It has a black imprint of Earth's land masses on it. If you peel the orange in one piece, you can try to make a flat map from the curved surface. Notice how the distances and shapes are distorted in the peeled orange.

STUDY TIP

Compare As you read, make a chart comparing the features of cylindrical, conic, and azimuthal map projections. Describe the way that each projection is made and what features it distorts.

The continents have been drawn on the peel of this orange.

This is what the peel of the orange looks like when it is flattened out. Notice how shapes and distances between points on the orange are distorted when the peel is flattened.

TAKE A LOOK

1. Explain Why do all maps

have distortions?

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SECTION 2 Mapping the Earth's Surface continued

READING CHECK

2. Define What is a map projection?

What Are Map Projections?

A map projection is a certain way of transferring the curved surface of the Earth to a flat map. Mapmakers use map projections to move the image of the Earth's curved surface onto a flat map.

To understand how map projections are made, think of a clear globe with a light inside it. If you wrap a piece of paper around the globe, the continents will make shadows on the paper. If you wrap the paper in different ways, the shadows will look different. Each way of wrapping the paper produces a different map projection.

There are four main kinds of map projections that mapmakers use--cylindrical, conic, azimuthal, and equalarea projections.

READING CHECK

3. Identify What are two distortions on a Mercator projection?

CYLINDRICAL PROJECTION A cylinder is a shape like a an empty paper-towel tube.

If you wrap the paper in a cylinder around the globe, the resulting map projection is called a cylindrical projection. The most common map projection is a cylindrical projection called a Mercator projection. In a Mercator projection, latitude and longitude lines are straight.

The Mercator projection has two main distortions. First, the space between longitude lines is equal everywhere, instead of being wider at the equator. Second, latitude lines are farther apart in the far north and south, instead of being evenly spaced everywhere.

The distortions in a cylindrical projection make areas near the poles look wider and longer than they really are. For example, the Mercator projection makes Greenland look larger than South America!

A cylindrical projection causes areas near the poles to look larger than they actually are.

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SECTION 2 Mapping the Earth's Surface continued

CONIC PROJECTION A cone is shaped like a party hat. If you wrap the paper

in a cone around one of the Earth's hemispheres, the resulting map projection is called a conic projection.

The cone touches the globe at each line of longitude. Therefore, a conic projection shows each longitude line accurately. However, the cone only touches the globe at one line of latitude. Areas on this line of latitude are not distorted. However, areas far from this latitude look distorted in a conic projection.

The distortions in a conic projection are worst from north to south. Therefore, conic projections are best for mapping land masses with more area east and west. They are good for mapping continents that are wide, such as the United States.

READING CHECK

4. Explain Why do conic projections show longitude accurately?

TAKE A LOOK

5. Identify Which parts of a conic projection are most distorted?

A conic projection causes more distortion from north to south than from east to west.

AZIMUTHAL PROJECTION If you place a flat piece of paper on top of the globe, the

resulting map projection is called an azimuthal projection. On an azimuthal projection, the plane touches the

globe at only one point. In most azimuthal projections, this point is one of the geographic poles. The distortion near this point is very small. However, distortions of direction, distance, and shape increase as you move away from this point.

Azimuthal projections are most often used to map areas that are near the North and South Poles. The figure at the top of the next page shows an azimuthal projection.

Critical Thinking

6. Infer Why are azimuthal projections most often used to map areas that are near the poles?

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

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Maps as Models of the Earth

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SECTION 2 Mapping the Earth's Surface continued

How Is Information Shown on Maps?

The information on a map is in the form of symbols. To read a map, you must understand the symbols on the map. Maps can show many different kinds of information. Almost all maps contain five pieces of information: a title, an indicator of direction, a scale, a legend, and a date.

Texas Road Map

READING CHECK

10. Describe How is information shown on a map?

The title tells you what the subject of the map is.

The indicator of direction can show which way is north or give other information about the location of the map. It can be a compass rose like this one, an arrow pointing north, or a latitude and longitude grid.

TAKE A LOOK

11. Identify What is the subject of the map in the figure?

The legend tells what the symbols on the map mean.

The scale shows how a distance on the map is related to the distance on the Earth.

Scale:

1:1,500,000

Legend

35 Interstate Route 81 U. S. Route

21 State Route

75 Highway Loop or Spur

21 Farm or Ranch to Market Road

P4 Park Road

R1 Recreational Road

The date tells you when the map was made. It may also tell you when the information in the map was collected.

?2003

Critical Thinking

12. Reason Why is it important for a map to have a legend?

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