Grids, Coordinates, Ordered Number Pairs

What They Are and How They Work

CoordinatesCoordinates are “ordered pairs” of numbers that we can use to help us find things and go places.

They are called ordered because they always come in the same order.

We can use coordinates to find things, a place on earth or on a map, to figure out how to get from one point to another, and to give us direction.

They look like this:(2,9) or (-3, 12) or (10, -14)

So how do the two numbers help me find anything?

By themselves they don’t. For them to work, you need a “grid.”

OK, so what’s a grid?

This is a grid.

So is thisgfe Xdcba

1 2 3 4 5 6

We will talk about this type of grid later when we learn about Graphs.

Lets look at the first grid type we saw.

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-14

-13-12

-11

-10

-9-8

-7

-6

-5

-4

-3

-1

-2

And if you add numbers to the grid,it looks like this.

Before we can understand why number on a grid are so important, we need to learn somenomenclature.

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-10

-9-8

-7

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-5

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-3

-1

-2

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-14

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-10

-9

-8

-7

-6

-5

-4

-3

-1

-2

The two lines that make the grid have names. They are called the Axis.

This is X axis.

X

Y

This is the Y axis.The point where the two lines cross is (0,0).

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-14

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-10

-9

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Notice that some of the numbers are positive numbers --

and some of the numbers are negative numbers.

Pay close attention

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-14

-13-12

-11

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-9-8

-7

-6

-5

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-1

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Now lets put a box around the grid.

+

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NO point has the same coordinates as

any other point!

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R

f

So? What does this mean?

It means that if you know the coordinates of a point on the grid you can find it

quickly and easily!

How?

Like this: suppose you are given (7,5) (14,-3) and (-4,-8)

all you need to remember is that you find the first number along the X axis

(remember that is the side-to-side axis) and the second number on the Y (up-

down) axis.

Let’s try it.

The secret of using a grid is to start at the

(0,0) point

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-14

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-9

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-5

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-1

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Next move left or right on the X axis until you find the first number in your coordinate pair.

Then move up or down on the Y axis until you locate the second number.

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-14

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-9

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-6

-5

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-1

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Using our first

coordinates (7,5)

First find 7 on the X axis

Then find 5 on the Y.

Then connect the dots.

(7,5)

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-14

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-11

-10

-9

-8

-7

-6

-5

-4

-3

-1

-2

Using our second pair of

coordinates (14,-3) First find 14 on the X axis

Then find -3 on the Y.

Then connect the dots.

(14,-3)

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-14

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-9

-8

-7

-6

-5

-4

-3

-1

-2

Using our last set of

coordinates (-4,-8)

First find -4 on the X axis

Then find –8 on the Y.

Then connect the dots.

Bingo! Now you’ve got it!

Got what? I still don’t get how this helps me find

anything.

(-4,-8)

So what does this have to do with

GEOGRAPHY?

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What if I do this!

Washington, D.C.

You

Do you see the grid?

Typical Graph

• This is an example of a typical graph we are all familiar with.

• The graph is made up of different “points” with lines that connect the points.

Typical Graph • X value is always stated first

• Followed by the Y value

• The “origin” is the point wherethe 2 axes intersect with a value of (0,0)(0,0)

(3,8)Y

X

(9,5)

The confusion comes when we extend the lines on the X and Y

axis around a sphere and call them Longitude and

Latitude.

Longitude Lines go through the poles.

Longitude and Latitude

Which is which?

Notice that these lines are the hash marks on the X axis

X Axis

Notice that these lines are the hash marks on the X axis

X Axis

Notice that these lines are the hash marks on the X axis

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X

Latitude lines go around the earth like a belt. Y axis

Latitude lines go around the earth like a belt. Y axis

How to remember which is which. Think of Laddertude

On a ladder you go up the rungs. Same with latitude.

See, Laddertude

The zero degrees mark of latitude is the Equator, and the zero

degrees mark of longitude is the Prime Meridian

0º, 0º

East West, North South on the Earth

• Let each of the four quarters then be designated by North or South and East or West.

N

S

EW

If you think about it for a minute, you will see that the equator

divides the earth into halves. A northern half, and a southern half. And that Prime Meridian creates East and West halves.

These two important lines divide the earth into Hemi (which means ½ ) spheres.

Here is another image of the Hemispheres

This makes it possible to think of the earth like this:

• The N tells us we’re north of the Equator.

The S tells us we’re south of the Equator.

• The E tells us that we’re east of the Prime

Meridian. The W tells us that we’re west of the Prime Meridian.

(N, W) (N, E)

(S, W) (S, E)

Two other important lines on earth.

The Tropics.

Tropic Lines

How are longitude and latitude

coordinates written and what do they

mean?

Longitude and latitude are measured in degrees, minutes, and seconds and look like this.

The location of Lanier on Earth is:

29º 44 30.14 N

95º 29 18.40 W

We have learned that 0º of Latitude is the Equator and 0º Longitude is the

Prime Meridian• So we know that both latitude

and longitude are measured in degrees.

• But how do you measure between degrees?

Each DEGREE is divided into MINUTES.

There are 60 MINUTES in each

DEGREE.

Each MINUTE is divided into SECONDS.

There are 60 SECONDS in each

MINUTE.

NOW FOR PRACTICE

You will use your atlas to find coordinates (longitude and latitude) then answer the question.

2. What African country are you in if you are at 10º S, 40º E ?

3. What major city is the nearest to 30ºN, 90º W?

4. What would you really need if you were at 1º S, 3º W

5. What type of clothing would you need if your position was 40ºN, 0º E in the winter?

1 . In S. America, what country are you in if you are at 10 degrees S, 50 degrees W

6. What would your latitude be if you were visiting Oslo, Norway?

7. How about Tokyo?

8. How about Perth, Australia?

Now do you see, if you have the coordinates of a place on a map, you can find the place

without spending hours looking all over.

Wow, what a great idea!