Locating Places on the Earth

Why This Matters

Imagine you arrive in a new city for the first time. You want to visit your cousin’s house. How will you find it?

You could ask someone on the road. Or you could look at a map on a phone. The map shows a small dot. “You are here,” it says. And it shows another dot for your cousin’s house.

But think about this. How does the phone know exactly where that house is, out of all the houses in the whole world?

The answer is simple and clever. Every single place on Earth has its own special “address” made of numbers. No two places share the same address. So we can point to any spot — a city, a village, even the middle of an ocean — and say exactly where it is.

In this chapter, you will learn how this address system works. You will learn how people pin down any place on our big, round Earth. By the end, you will be able to read the “address” of any city. It is like a treasure map for the whole planet.

The Big Idea

The Earth is shaped almost like a ball. To find any place on it, we use two sets of imaginary lines drawn all over the globe. One set runs side to side (these are latitudes) and tells us how far north or south a place is. The other set runs top to bottom (these are longitudes) and tells us how far east or west a place is. When one line from each set crosses, they point to one exact spot — just like two crossing roads point to one exact corner. Together, those two numbers are the place’s address on Earth.

Let’s Break It Down

We will go step by step. First, let us look at the shape of the Earth and the simple idea of directions. Then we will build up to the lines that give every place its address.

The globe and directions

Our Earth is very big. We cannot see its whole shape from the ground. But people have found out that the Earth is round. It is shaped almost like a ball. A ball shape is called a sphere. (A sphere just means a perfectly round shape, like a football or an orange.)

We say almost a sphere because the Earth is not perfectly round. It is squashed a tiny bit at the top and the bottom. But this is so small that, for our work, we can treat it as a ball.

A globe is a small model of the Earth. It is a small ball on which a map of the Earth is drawn. Because the globe is round just like the Earth, it shows the shape of land and sea truly. A flat paper map cannot do this perfectly. (Try peeling an orange in big pieces and pressing the peel flat — it tears. You cannot flatten a round thing without tearing or stretching it. That is why a round globe shows the Earth better than a flat map.)

Figure 1.1 below shows the shape of the Earth and how a globe copies it.

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Now, to talk about where things are, we need directions. You already use directions in daily life. You say “the temple is up that way” or “the market is behind us.” But for maps we need exact directions.

There are four main directions. They are North, East, South and West. We can remember them with the short letters N, E, S, W. On most maps, North is at the top.

These four are called the cardinal directions. (The word “cardinal” just means “main” or “most important” here.)

But what if a place is not exactly north, and not exactly east, but somewhere in between? For that we have four in-between directions. They sit between the main ones:

• Northeast (NE) — between North and East
• Southeast (SE) — between South and East
• Southwest (SW) — between South and West
• Northwest (NW) — between North and West

The picture below, Figure 1.2, shows all eight directions together. It is called a compass rose because the lines spread out like petals of a flower (a “rose”).

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Here is a tiny everyday example. Suppose your school is to the North of your home. And the bus stop is to the East. Then a place that is up-and-to-the-right of your home — between the school and the bus stop — would be in the Northeast direction. That is how the in-between directions help us be more exact.

Latitudes (parallels) — Equator, Tropics, Poles

Now we come to the clever lines drawn on the globe.

First, let us find two special points. Spin a globe slowly. You will see that two points do not move much — one at the very top and one at the very bottom. These two fixed points are called the poles. The top one is the North Pole. The bottom one is the South Pole.

Exactly halfway between the two poles, there is a line that runs all the way around the middle of the Earth, like a belt around the tummy. This middle line is called the Equator.

Now imagine you start at the Equator and walk towards the North Pole. With every step, you get a little farther from the Equator. To measure how far you are from the Equator, we use latitude.

At any point on your walk, you can draw an imaginary line that goes all the way around the Earth, running east and west, side by side with the Equator. Each such line is called a parallel of latitude. (“Parallel” means the lines stay the same distance apart and never meet, like the two rails of a railway track.)

We measure latitude in degrees. A degree is just a unit for measuring, and we write it with a small circle, like this: 23.5°. Here is how the numbers work:

• The Equator is the starting line, so it is 0° (zero degrees).
• As you go up towards the North Pole, the number grows, until the North Pole is 90°N (ninety degrees North).
• As you go down towards the South Pole, the number grows the other way, until the South Pole is 90°S (ninety degrees South).

Two of these parallels have special names you should know:

• The Tropic of Cancer, at about 23.5°N (a bit above the Equator).
• The Tropic of Capricorn, at about 23.5°S (a bit below the Equator).

Figure 1.3 below shows the Equator, the Tropics and the poles on a globe. Notice one important thing in it.

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Did you notice it? The Equator is the biggest circle. As the parallels go up or down towards the poles, they get smaller and smaller. Right at the poles, a “circle” shrinks to a single point. That is just how a ball is shaped — slices near the middle are wide, and slices near the top or bottom are tiny.

Latitude even tells us a little about the weather. Why? Let us think about it simply.

So, a single latitude line tells us how far north or south a place is. But is that enough to find a place? Not yet. Let us see why, with the next set of lines.

Longitudes (meridians) — the Prime Meridian

A latitude line goes all the way around the Earth. So if I only say “this place is at 29°N,” that line passes through many countries! It passes through India, but also through other lands far away. One number alone is not enough.

So we need a second set of lines. These run the other way — from the North Pole straight down to the South Pole.

Imagine you start at the North Pole and travel by the shortest path to the South Pole. That path is half of a circle. Such a line is called a meridian of longitude. All meridians are half-circles. They all start at the North Pole and end at the South Pole. So they all meet at the two poles.

Longitude measures how far east or west a place is. But east or west of what? We need a starting line, just like the Equator was the starting line for latitude.

For longitude, the starting line is called the Prime Meridian. (“Prime” means “first.”) It is also called the Greenwich Meridian, because it passes through a place called Greenwich, in the city of London, in England. Long ago, in the year 1884, many countries agreed together that this line would be the world’s starting line for longitude. The Prime Meridian is marked as 0° longitude.

From the Prime Meridian, longitude grows as you go east, and it also grows as you go west:

• Going east, the number rises from 0° up to 180°E.
• Going west, the number rises from 0° up to 180°W.

There is one neat fact. The line at 180°E and the line at 180°W are actually the same line, sitting right opposite the Prime Meridian on the other side of the Earth. So that one line is simply written as 180°, with no E or W.

Figure 1.4 below shows the meridians and the Prime Meridian on a globe.

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So now we have two sets of lines. Latitudes run side to side. Longitudes run top to bottom. Together they cover the whole globe with a criss-cross pattern. This pattern of crossing lines is called the grid, and the lines are called grid lines. The grid is what lets us find any place. Let us see how.

Hemispheres

Before we find places, here is a useful word: hemisphere. “Hemi” means “half.” So a hemisphere is one half of the Earth.

The Earth gets cut into halves by our two main starting lines.

The Equator cuts the Earth into a top half and a bottom half:

• The top half is the Northern Hemisphere.
• The bottom half is the Southern Hemisphere.

The Prime Meridian (with its opposite line, 180°) cuts the Earth into a left half and a right half:

• The right half is the Eastern Hemisphere.
• The left half is the Western Hemisphere.

Figure 1.5 below shows both of these splits side by side.

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So every place lives in two halves at once. India, for example, is in the Northern Hemisphere (above the Equator) and in the Eastern Hemisphere (east of the Prime Meridian). This is why we write India’s longitude with an “E.”

Finding a place with latitude + longitude

Now for the fun part. We can give any place its exact address.

Think about a row of shops in a market. If a friend says “meet me at a shop in the market,” that is not enough — there are many shops! But if your friend says “the 7th shop in the 5th row,” now you know exactly which one. Two numbers fix one shop.

It is the same idea on Earth. One latitude line passes through many places. One longitude line also passes through many places. But there is only one spot where a chosen latitude line and a chosen longitude line cross each other. That crossing point is the exact place.

So the “address” of a place is just two numbers: its latitude and its longitude. These two numbers are called the coordinates of the place.

Figure 1.6 below shows this crossing idea clearly.

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This is exactly why one number is never enough. Latitude alone gives a whole circle around the Earth. Longitude alone gives a whole half-circle from pole to pole. Only the crossing of one of each gives a single point. Two numbers, one place.

Let us write this as a quick reminder, because latitudes and longitudes are easy to mix up.

Many of these facts come from earlier ideas about lines and circles. Here is a quick refresher so nothing feels new.

Now let us use these two numbers to actually find a place, step by step.

That is the whole secret. Give me any two numbers — a latitude and a longitude — and I can point to one exact place anywhere on Earth. The whole planet has been turned into a giant, neat grid.

Common Mistakes

Let us clear up a few things that often confuse students. For each one, see why it feels right, and then the correct idea.

Quick Check

Try these quick questions. Read each one, pick your answer, and then read why.

Practice Problems

Now try these on your own. Think first, then tap to check the full answer.

Easy

Medium

Challenge

Summary

Here are the key things you should now be able to explain in your own words:

• The Earth is shaped almost like a ball (a sphere), squashed a little at the top and bottom. A globe is a small model of it.
• The four main directions are North, East, South and West. The four in-between ones are NE, SE, SW and NW.
• Latitudes (also called parallels) run side to side. They are full circles. The Equator is the 0° starting line; the poles are at 90°N and 90°S.
• Longitudes (also called meridians) run from pole to pole. They are half-circles that meet at the poles. The Prime Meridian (through Greenwich) is the 0° starting line; values go up to 180°E and 180°W.
• The Equator splits Earth into the Northern and Southern Hemispheres. The Prime Meridian splits it into the Eastern and Western Hemispheres.
• To find any place, we use its two numbers — latitude and longitude, called its coordinates. Only where one latitude line crosses one longitude line is there a single exact spot. That is why we always need both.

What’s Next

You can now pin down any place on Earth using its address of two numbers. But what exactly are we pointing at? Most of our planet is not land at all — it is water.

In the next chapter, Chapter 2 — Oceans and Continents, we will zoom out and look at the big picture of the Earth’s surface: the huge stretches of land called continents, and the vast bodies of water called oceans. Get ready to explore the whole face of our planet.