CHAPTER 2 SECTION 1 You Are Here - Weebly

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CHAPTER 2

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Maps as Models of the Earth

SECTION

1 You Are Here

BEFORE YOU READ

After you read this section, you should be able to answer

these questions:

? What is a map?

? What are latitude and longitude?

? How can you find locations on Earth?

What Is a Map?

A map is a model that shows the features of an object. Most

maps that people use show the features of Earth¡¯s surface.

Some maps show all of the Earth¡¯s surface. Other maps show

only part of it. Maps can show natural features, such as rivers.

They can also show features made by people, such as roads.

STUDY TIP

Discuss Read this section

quietly to yourself. In a small

group, try to ?gure out anything you didn¡¯t understand.

FINDING DIRECTIONS ON EARTH

The Earth¡¯s shape is similar to a sphere, but the Earth

is not a true sphere. A true sphere has no top, bottom, or

sides¡ªit looks the same from all directions. In addition, a

true sphere has no reference points. Reference points are

certain locations that never change. They can be used to

define directions.

Unlike a true sphere, the Earth has two reference points.

They are located where the Earth¡¯s axis of rotation passes

through the Earth¡¯s surface. The reference points are called

the North Pole and the South Pole. The North and South

Poles are known as geographic poles. Since these poles

never move, they are used as reference points to define

directions on Earth.

READING CHECK

1. De?ne What are

reference points?

Earth¡¯s axis

of rotation

North Pole

The North Pole and the

South Pole can be used

as reference points to

de?ne directions on

Earth.

TAKE A LOOK

2. Identify What are two

reference points on Earth?

South Pole

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CARDINAL DIRECTIONS

READING CHECK

3. Identify What are the four

cardinal directions?

READING CHECK

4. Describe In which general

cardinal direction does a

compass needle point?

A reference point alone will not help you give good

directions. You also need to describe how to get from

one place to another. To do this, you can use the cardinal

directions. The cardinal directions are north, south, east,

and west. To use cardinal directions properly, you will

need to use a compass.

USING A COMPASS TO FIND DIRECTIONS

The Earth is like a giant magnet. It has two magnetic

poles, which are located near the geographic poles. You

can use the magnetic poles to help you find the cardinal

directions.

A compass is a tool that uses the Earth¡¯s natural

magnetism to show direction. The needle on a compass

points to the magnetic pole that is near the geographic

North Pole. Therefore, you can use a compass to learn

which direction is north.

TRUE NORTH AND MAGNETIC DECLINATION

There is a difference between the location of the

geographic North Pole and the magnetic pole. Therefore,

a compass needle cannot show you exactly where the

geographic North Pole is. When you use a compass,

you have to correct for this difference. True north is

the direction of the geographic North Pole. The angle

between true north and the direction a compass needle

points is called magnetic declination.

Magnetic declination

True north

TAKE A LOOK

5. De?ne What is true

north?

Geographic

North Pole

Geographic

South Pole

The magnetic and geographic

poles are not in the same place.

Therefore, compass readings must

be corrected to learn the direction

of true north.

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USING MAGNETIC DECLINATION

Magnetic declination is measured in degrees east

or west of true north. The magnetic declination is different for different points on the Earth¡¯s surface. Once

you know the declination for your area, you can use a

compass to determine the direction of true north. For

example, suppose the magnetic declination in your area

is 10¡ãW. This means that true north is 10¡ãE of the

direction a compass needle points.

21?

20?

19?

18?

17?

16?

Critical Thinking

6. Apply Concepts The

magnetic declination for an

area is 8?E. Compared to the

direction a compass needle

points, in which direction

does true north lie?

24?

22?

20?

18?

16?

14?

15?

12?

14?

13?

12?

10?

8?

11?

6?

10?

0? 2?

9?

8?

7? 6? 5?

2?

4? 3?

4?

1?

TAKE A LOOK

7. Read a Map Roughly what

is the magnetic declination in

the area in which you live?

The lines on this map connect points that have the same magnetic declination.

How Do People Find Specific Locations

on Earth?

All of the houses and buildings in your neighborhood

have addresses that give their locations. These addresses

may include a street name and a number. You can tell

someone exactly where you live by giving them your

address. In a similar way, you can use latitude and longitude to give an ¡°address¡± for any place on Earth.

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LATITUDE

READING CHECK

8. De?ne What are parallels?

The equator is a circle halfway between the North

and South Poles. It divides Earth into two hemispheres,

or halves¡ªthe Northern Hemisphere and the Southern

Hemisphere. Lines of latitude, or parallels, are imaginary

lines on Earth¡¯s surface that are parallel to the equator.

Latitude is the distance north or south from the equator. Latitude is measured in degrees. The equator represents 0¡ã latitude. The North Pole is 90¡ã north latitude and

the South Pole is 90¡ã south latitude. North latitudes are in

the Northern Hemisphere and south latitudes are in the

Southern Hemisphere.

.ORTH 0OLE

?.

%QUATOR

.ORTHERN

(EMISPHERE

?.

?.

?.

?

?3

TAKE A LOOK

?3

9. Describe Which parallel

is farther from the equator:

10? N latitude or 10? S latitude?

?3

0ARALLELS

3OUTHERN

(EMISPHERE

3OUTH 0OLE

?3

LONGITUDE

Lines of longitude, or meridians, are imaginary lines

that link the geographic poles. Lines of longitude are

similar to the lines on a basketball. The lines all touch

at the poles. They are farthest apart at the equator. The

prime meridian is the line that represents 0¡ã longitude.

Longitude is the distance east or west of the prime

meridian. Like latitude, longitude is measured in degrees.

The prime meridian does not circle the whole globe. It

runs from the North Pole, through Greenwich, England,

to the South Pole. On the other side of the globe, the 180¡ã

meridian runs from the North to the South Pole. Together,

the prime meridian and the 180¡ã meridian divide the

Earth into Western and Eastern Hemispheres.

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Critical Thinking

.ORTH

0OLE

?

MERIDIAN

?7

7

?7

?7



?7

?%



?



7ESTERN

(EMISPHERE

10. Apply Concepts A friend

asks you what the distance is

between 80?E longitude and

90?E longitude. What else do

you need to know in order to

answer your friend¡¯s question?

Explain why you need this

piece of information.

%ASTERN

?% (EMISPHERE

?

%

0RIME

MERIDIAN

3OUTH

0OLE

USING LATITUDE AND LONGITUDE

Lines of latitude and longitude cross to form a grid. This

grid is shown on maps and globes. You can use the lines of

latitude and longitude to tell someone the location of any

point on the Earth¡¯s surface. First, find the point on a map

like the one below. Then, estimate the latitude and longitude

of the point, using the lines closest to it.

45¡ãN

40¡ãN

35¡ãN

30¡ãN

25¡ãN

120¡ãW 115¡ãW 110¡ãW 105¡ãW 100¡ãW 95¡ãW

TAKE A LOOK

90¡ãW

85¡ãW

80¡ãW

75¡ãW

You can use latitude and longitude to locate points on a map. For example,

this city is located very close to latitude 35?N, longitude 105?W.

11. Read a Map Circle

the city on the map that

is closest to latitude 45?N,

longitude 100?W.

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