Exploring Society · Chapter 1 — Locating Places on the Earth

Suppose you get off a train in a town you have never visited and you want to reach a bank. You could ask someone on the road, or you could open a map on paper or on a phone. In a few seconds the map shows you where you are, where the bank is and which roads join the two. That is the power of a map.

What a map is. A map is a drawing of an area of the Earth's surface, seen as if you were looking straight down on it from above, like a bird flying overhead. The area can be very small, such as a village, a school or a park. It can be larger, such as a district or a state. It can even be very large, such as the whole of India or the whole world.

An atlas. A book that collects many maps together is called an atlas. Your school atlas may have maps of India, of each continent and of the world.

Three common kinds of maps. Maps are made for different purposes, so they show different things:

A map is like a treasure guide. It tells you where things are and how to get from one place to another. But to use a map well, you must know how to read its three main parts, or components: distance, direction and symbols. We study each of them in the next two topics.

Why maps matter. Drivers, pilots, ship captains, soldiers, farmers planning water channels, town planners and even delivery riders use maps every day. When your family uses a phone app to find a shop, it is reading a map made from careful measurements of the Earth.

Try it. Draw a simple map of your classroom as if you were a fly on the ceiling. Show the door, the windows, the teacher's table and the rows of desks. Then compare your map with a friend's map. Which things did both of you show? Which things did one of you leave out?

How can a whole country fit on one page of your atlas? The secret is the scale. Everything on the map is drawn many times smaller than it really is, but always shrunk by the same amount.

What scale means. The scale of a map tells us how a distance on the map compares with the real distance on the ground. If 1 centimetre on the map stands for 500 metres on the ground, we write the scale as 1 cm = 500 m. A map of India in a textbook may use a much bigger jump, such as 2.5 cm = 500 km, shown as a small ruler (a scale bar) in a corner of the map.

How to use a scale. There are just three steps:

• Measure the distance between the two places on the map with a ruler.
• Find out how much ground distance 1 cm stands for.
• Multiply: map distance x ground distance for 1 cm = real distance.

Example 1. On a town map with scale 1 cm = 500 m, the station and the bank are 4 cm apart. The real distance is 4 x 500 m = 2,000 m, which is 2 km.

Example 2. On a map of India with scale 2.5 cm = 500 km, first find what 1 cm means: 500 / 2.5 = 200 km. If two cities are 5 cm apart on that map, they are 5 x 200 = 1,000 km apart on the ground.

Drawing to scale. Scale also works the other way round. To draw a playground 40 m long and 30 m wide with a scale of 1 cm = 10 m, divide each real length by 10: the rectangle on paper will be 4 cm by 3 cm. If you measure its diagonal with a ruler, you get 5 cm, so the real diagonal is 5 x 10 = 50 m.

Large and small areas. A map of a small area, like your school, can show a lot of detail: every room and tree. A map of a big area, like the world, has to leave out small details, because everything is shrunk so much.

Careful with units. Always check whether the scale is in metres or kilometres. Remember that 1 km = 1,000 m, so 2,000 m is the same as 2 km.

If a friend tells you 'the shop is 2 km away', you still do not know where to go. You also need to know which way. That is why every good map shows direction.

Cardinal directions. The four main directions are north, east, south and west. They are called the cardinal directions or cardinal points. On most maps north is at the top. Moving clockwise from north you meet east, then south, then west. Many maps simply show a small arrow with the letter N to mark north; from it you can work out the others.

Intermediate directions. Between the cardinal directions lie four more: northeast (NE) between north and east, southeast (SE), southwest (SW) and northwest (NW). Together they make eight directions, often drawn as a compass rose.

Finding direction in real life. In the morning the Sun rises roughly in the east. If you stand facing the rising Sun, east is in front of you, west is behind you, north is on your left and south is on your right. A magnetic compass also shows north.

Symbols. On the map of a large city or a whole country, there is no room to draw every building, road and tree. So map makers use small signs called symbols. A short line pattern can stand for a railway, a small cross or building shape for a place of worship, blue lines for rivers and canals, and letters such as PO for a post office and PS for a police station. Colours help too: blue for water, green for forests or low land, brown for hills.

Common symbols. So that everyone reads maps the same way, each country fixes a standard set of symbols. In India, the Survey of India, a government body, has fixed the symbols used on maps of India. Different countries may use somewhat different sets.

The key or legend. A box on the map, called the key or legend, explains what each symbol and colour means. Before reading any map, look at its legend first.

Putting it together. With distance (scale), direction (the north arrow) and symbols (the legend), you can read almost any map: 'Go 1 km northeast from the station; the school is just past the canal.'

Peel an orange carefully so that the skin comes off in three or four big pieces, and then try to press the pieces flat on a table. They tear at the edges. This simple test shows a big problem for map makers: the Earth is round, but paper is flat.

The shape of the Earth. The Earth is very nearly a sphere, like a ball. It is slightly flattened at the North and South Poles, but for our study we can treat it as a sphere. A round surface cannot be laid flat on paper without stretching or tearing some parts, so every flat world map changes some shapes or sizes a little.

The globe. A globe is a sphere on which a map is drawn. It is usually made of plastic, metal or cardboard and turns on a tilted stand. Because a globe has the same round shape as the Earth, it shows the shapes, sizes and positions of continents and oceans more truly than a flat map. Globes can also show the Moon, other planets or the stars in the sky.

Saying exactly where something is. Imagine a big market with neat rows of shops of the same size. You tell a friend, 'Meet me at the 7th shop in the 5th row.' With just two numbers your friend can find the exact shop. A chessboard works the same way: its columns are named a to h and its rows 1 to 8, so every square has a name such as d4 (column d, row 4).

Coordinates. A pair of values that fixes the position of a place like this is called a set of coordinates. One value tells you how far along in one direction, the other how far along in a direction at right angles to the first.

Coordinates on the Earth. Map makers use the same idea for the Earth. They draw two sets of imaginary lines on the globe: lines running east to west, called parallels of latitude, and lines running from pole to pole, called meridians of longitude. Together they form a net or grid. Any place on Earth can then be named by two numbers, its latitude and its longitude. The next topics explain each one.

Spin a globe slowly. Two points stay still: the top and the bottom. These are the North Pole and the South Pole. Halfway between them, a line runs right around the middle of the globe. This is the Equator.

What latitude measures. Imagine you stand on the Equator and walk towards the North Pole. The further you go, the further you are from the Equator. Latitude tells how far north or south of the Equator a place is.

Parallels of latitude. At every point of your walk, you could draw a line running east to west, parallel to the Equator. Such a line goes right round the Earth as a circle and is called a parallel of latitude. The Equator is the biggest of these circles. Moving towards either pole, the circles become smaller and smaller, until at the pole the circle shrinks to a single point.

Measuring in degrees. Latitude is measured in degrees (°). The Equator is 0°. The North Pole is 90°N and the South Pole is 90°S. Every place north of the Equator has a latitude marked N, and every place south of it has a latitude marked S. A degree of latitude can be pictured as an angle at the centre of the Earth, measured from the plane of the Equator.

Hemispheres. The Equator divides the Earth into two halves. The half to the north is the Northern Hemisphere; the half to the south is the Southern Hemisphere. India lies wholly in the Northern Hemisphere, between about 8°N and 37°N.

Latitude and climate. Latitude is closely linked with how hot or cold a place usually is:

You will learn in Science why the Sun heats places near the Equator more strongly and why seasons change during the year.

Imagine travelling from the North Pole to the South Pole along the shortest path. You could pass through Europe and Africa, or through Asia, or across the Pacific Ocean. Each such path is the same length. These pole-to-pole lines are the meridians of longitude.

Meridians. Each meridian is a half-circle running from the North Pole to the South Pole. Unlike parallels, all meridians are the same length, and they all meet at the two poles.

A starting line: the Prime Meridian. To measure longitude we need a zero line. In 1884, several nations agreed that the meridian passing through Greenwich, an area of London in England, would be the international zero line. It is called the Prime Meridian or Greenwich Meridian and is marked 0° longitude.

Measuring longitude. Longitude tells how far east or west of the Prime Meridian a place is. It is measured in degrees from 0° to 180° towards the east (marked E) and from 0° to 180° towards the west (marked W). 180°E and 180°W are the same line, so it is simply written 180°. Rounded off, New York is at about 74°W, Delhi at about 77°E and Tokyo at about 140°E.

Eastern and Western Hemispheres. The Prime Meridian and the 180° line together divide the Earth into the Eastern Hemisphere and the Western Hemisphere. India is in the Eastern Hemisphere and also in the Northern Hemisphere.

Using both coordinates. Now we can name any place with two values. 'Delhi lies at about 29°N, 77°E' means: 29 degrees north of the Equator and 77 degrees east of the Prime Meridian. India stretches from about 8°N to 37°N in latitude and from about 68°E to 97°E in longitude.

India's own prime meridian. Greenwich was not the first zero line. Many centuries earlier, Indian astronomers used a prime meridian called the madhya rekha ('middle line'), which passed through Ujjayini, today's Ujjain, a famous centre of astronomy. The astronomer Varahamihira worked there about 1,500 years ago. Indian astronomical texts used this meridian as their reference for calculations.

When it is breakfast time in India, it is still the night before in New York. How can the same moment have different times? The answer lies in the Earth's spin.

15 degrees every hour. The Earth spins from west to east and makes one full turn, 360°, in about 24 hours. So in one hour it turns 360 / 24 = 15°. This means each 15° of longitude makes a difference of 1 hour in local time, and each 1° makes a difference of 60 / 15 = 4 minutes.

Local time. The local time of a place is set by the Sun: it is noon when the Sun is highest in the sky there. Places to the east see the Sun earlier, so their local time is ahead. If it is 12 noon at Greenwich (0°), it is 1 pm at 15°E and 2 pm at 30°E, but 11 am at 15°W and 10 am at 30°W.

A problem inside one country. Porbandar in Gujarat and Tinsukia in Assam are roughly 30° of longitude apart. 30 x 4 = 120 minutes, so local time in Tinsukia is about 2 hours ahead. That is why the Sun can set in Assam while it is still full daylight in Gujarat. If every town kept its own local time, train timetables and phone calls would be very confusing.

Standard time. So most countries choose one meridian and use its local time everywhere. This is called standard time. Indian Standard Time (IST) is 5 hours 30 minutes ahead of Greenwich Mean Time (GMT). That matches the meridian of 82.5°E, because 82.5 x 4 = 330 minutes = 5 hours 30 minutes. So when it is 12 noon in London (GMT), it is 5:30 pm in India.

Time zones. The world is divided into time zones, roughly 15° wide. Their borders are not straight lines because they bend to follow the borders of countries. Very large countries need more than one zone: the USA uses six and Russia uses eleven.

The International Date Line. Opposite the Prime Meridian, near 180°, runs the International Date Line. Crossing it, you change the date: travelling eastward across it you go back one day (say Monday to Sunday), and travelling westward you go forward one day (Sunday to Monday). The line bends in places so that no country is split into two different dates.