Locating Places on Earth

A map is a drawing of some area as seen from above. It can cover a small area (a village, a town), a bigger one (a district or state), or a very large one (India, or the whole world).

There are three important components of every map:

1. Distance — handled through the scale
2. Direction — handled through the cardinal points
3. Symbols — handled through a standard symbol set

A map is like a treasure guide: it shows you where things are and how to get to them.

A huge place fits onto a small sheet of paper thanks to the map’s scale. Each centimetre on the map stands for a fixed distance on the ground.

• If the scale is 1 cm = 500 m, then 3 cm on the map means 1,500 m on the ground.
• On the map of India (Fig. 5.2), the scale is drawn as a ruler with ‘500’ above it and ‘km’ beside it. That ruler measures 2.5 cm in print and represents 500 km on the ground.

The actual distance between two points on a map therefore depends entirely on the scale being used.

North is at the top of the map. Moving clockwise from north: east, south, west. These four are the cardinal directions (or cardinal points).

Between them lie the intermediate directions: northeast, southeast, southwest, northwest. Most maps simply carry an arrow marked ‘N’ pointing north.

           North
   Northwest  |  Northeast
            \ | /
    West ---- + ---- East
            / | \
   Southwest  |  Southeast
           South

On the map of a large city or a country there is not enough room to draw every building. Instead a symbol stands for each feature — buildings (railway station, school, post office), roads and railway lines, and natural elements (a river, a pond, a forest). This packs a great many details into a small space.

Different countries use different symbol sets. In India the Survey of India, a government body, has fixed the standard set.

Mapping the Earth is harder than mapping a town, because the Earth is not flat — it is nearly a sphere. (‘Nearly’, because it is slightly flattened at the poles; in practice we treat it as spherical.)

A sphere cannot be shown accurately on a flat sheet of paper. Try the orange-peel test: peel an orange into three or four large pieces and flatten them on a table — you cannot do it without tearing them at the edges.

A globe is a sphere with a map drawn on it. Because the globe and the Earth share the same spherical shape, a globe represents the Earth’s geography better than a flat map does.

Two everyday examples show the idea:

• The market. “Meet me at 6 pm at the 7th shop in the 5th row from the entrance.” Two numbers fix the shop exactly.
• The chessboard. Letters a–h run along one side and numbers 1–8 along the other, so every square has a name. When White opens by pushing the queen’s pawn two squares forward, the pawn is said to have moved from d2 to d4.

In both cases two values together pin down one position. This is a system of coordinates, and the same idea is used on maps to locate any place on Earth.

Spin the globe: the two fixed points are the poles, and halfway between them runs the Equator.

Stand on the Equator and walk towards a pole — your distance from the Equator grows. Latitude measures that distance. At any point on the journey you can draw an imaginary line running east and west, parallel to the Equator; this is a parallel of latitude, and it forms a circle around the Earth.

• The Equator is the largest of these circles.
• The parallels grow smaller as you move north or south.
• Latitudes are given in degrees: the Equator is 0°, the North Pole 90°N, the South Pole 90°S.

Travel from the North Pole to the South Pole by the shortest line. You could go through Europe and Africa, or equally through Asia — the distance is the same. These lines are the meridians of longitude, and they are all half-circles running pole to pole.

Why longitude gives us time

The Earth spins on its axis. Imagine a desk lamp as the Sun shining on a globe: as the globe turns eastward, it is morning in some places, midday, evening or night in others — breakfast time in one country is lunchtime in another while a third is fast asleep. So measuring a place’s longitude also measures the time there.

The reference line

Longitude is measured from the Prime Meridian, marked 0°. It is also called the Greenwich Meridian because in 1884 some nations agreed that the meridian through Greenwich, an area of London in England, would be the international standard.

• Longitude increases from 0° to 180° going either west or east, with ‘W’ or ‘E’ added.
• Examples in round figures: New York 74°W, Delhi 77°E, Tokyo 140°E.
• 180°W and 180°E are the same meridian, so it is written simply as 180°.

Coordinates. Latitude and longitude together are the two coordinates of a place — “Delhi lies at 29°N latitude and 77°E longitude” (rounded, not exact).

All the parallels and meridians together form a grid over the globe (also called grid lines). This grid is what lets us define any location precisely.

• The Prime Meridian divides the Earth into the Western and Eastern Hemispheres.
• The Equator divides it into the Northern and Southern Hemispheres.

The Greenwich Meridian was not the first prime meridian. Many centuries before Europe, India had its own, called madhya rekhā (‘middle line’). It passed through the city of Ujjayinī (today Ujjain), a renowned centre of astronomy for many centuries. The famous astronomer Varāhamihira lived and worked there some 1,500 years ago.

Indian astronomers already understood latitude and longitude, including the need for a zero meridian, and the Ujjayinī meridian became the reference for calculations in all Indian astronomical texts.

The Earth rotates west to east, making a full turn every 24 hours. A full turn is 360°, so the Earth turns 15° every hour (15 × 24 = 360).

Mark meridians every 15° eastward from the Prime Meridian — 0°, 15°E, 30°E, 45°E … up to 180°E. Each step is the same as adding one hour of local time:

Every meridian has its own local time, but it would be hopelessly inconvenient for one country to run on many local times. So most countries adopt a single standard time, based on a meridian passing through the country.

These standard times are organised into time zones, which broadly follow the 15° bands. But on the world map the dividing lines are not straight — they bend to respect each country’s standard time and so tend to follow international borders.

The number written inside a country on a time-zone map is the hours to be added to GMT (positive sign) or subtracted from GMT (negative sign).

Opposite the Prime Meridian, at approximately 180° longitude, lies the International Date Line. The +12 and −12 time zones touch each other along it.

Cross it by ship or plane and you change the date:

It is only approximately at 180°, because it deviates in places to avoid splitting a country into two different dates.

It is 12 noon at Greenwich. What is the local time at 45°E?

1. Difference in longitude from the Prime Meridian = 45°
2. Time difference = 45 ÷ 15 = 3 hours
3. 45°E lies east of Greenwich, so the time is ahead → add 3 hours
4. 12 noon + 3 hours = 3 pm

Two friends talk on the phone in the late afternoon. The one in Tinsukia (Assam) says the sun has set and it is dark; the one in Porbandar (Gujarat) says it is still full daylight. Why? Taking the difference in longitude as 30°, what is the difference in local time?

1. Assam lies far to the east of Gujarat. The Earth spins west to east, so eastern places see the Sun rise — and set — earlier.
2. Difference in local time = 30 ÷ 15 = 2 hours
3. So Tinsukia’s local time is about 2 hours ahead of Porbandar’s. Sunset there happens roughly 2 hours earlier, which is why it is already dark in Assam while Gujarat still has daylight.
4. Both, however, set their clocks to the same IST — which is exactly why standard time differs from local time.

IST is defined as GMT + 5 hours 30 minutes. When it is 12:00 noon GMT in London, Indian clocks read 12:00 + 5:30 = 5:30 pm.

Delhi is at 29°N, Bengaluru at 13°N; both are at about 77°E. What is the difference in their local time?

1. Local time depends only on longitude, not latitude.
2. Both cities share almost the same longitude (77°E), so the difference in longitude ≈ 0°.
3. Difference in local time = 0 ÷ 15 = practically nil.
4. Their very different latitudes affect climate, not time.

A map has the scale 2.5 cm = 500 km. Two river estuaries are 7.5 cm apart on the map. What is the real distance?

1. 2.5 cm = 500 km, so 1 cm = 500 ÷ 2.5 = 200 km
2. Real distance = 7.5 × 200 = 1,500 km

A picture-map of a small city. Visible features: a railway station at the left with the railway line curving in, a school at the bottom left, a hospital (marked with a red cross) in the middle, a market with striped stalls below it, apartments along the top, a small lake and stream, the Nagar Panchayat building, a bank to the right of it, a museum at the lower right, and an orchard/field at the top right. Roads connect them all. Four arrows in the top right corner show N, E, S, W.

The Survey of India symbol set, paired as label → symbol: railway line (broad gauge, metre gauge) and railway station; roads (metalled, unmetalled); boundaries (international, state, district); river, well, tank, canal, bridge; temple, church, mosque, chhatri; Post Office (PO), Post & Telegraph Office (PTO), Police Station (PS); settlement and graveyard; trees and grass.

A globe centred on Africa and Europe. The Equator is marked across the middle at 0°, with 30°N, 60°N and the North Pole 90°N above, and 30°S below. The Prime Meridian runs vertically at 0°, with West Longitude (30°W, 60°W) to the left and East Longitude (30°E, 60°E, 90°E) to the right. Labelled land masses: North America, Europe, Asia, Africa; oceans: Atlantic, Indian.

Three small globes side by side. The first shows the Greenwich Meridian and the Equator together. The second shows the Prime Meridian splitting the Earth into Western and Eastern Hemispheres. The third shows the Equator splitting it into Northern and Southern Hemispheres.

A map of India with a dashed vertical line at 75.8°E — the ancient Ujjayinī meridian. Ancient cities (marked with a circle) named in astronomical texts as lying on it: Kurukṣhetra, Rohitaka/Rohtak, Mālavangara/Nagar, Ujjayinī/Ujjain, Māhiṣhmati/Maheshwar, and Kumārī/Kanyakumari. Modern cities (marked with a square) shown for reference: Delhi, Kolkata, Mumbai, Chennai, Bengaluru. Some ancient cities sit very close to the line and others a little off it, because measuring longitude needed accurate timekeeping, which was less precise then.

A graph with longitudes along the bottom (45°W, 30°W, 15°W, 0°, 15°E, 30°E, 45°E) and local time along the top (9 AM, 10 AM, 11 AM, 12 PM, 1 PM, 2 PM, 3 PM), referenced to the Prime Meridian at 0°. Each coloured band is a zone of 15° centred on a meridian, with the 15° width marked by a double-headed arrow.

A world map divided into vertical time-zone bands, with the offset from GMT written inside various countries (e.g. India +5.5, Russia showing +3 through +11, USA and Brazil showing negative values). Labels include Greenland, UK, Europe, Africa, Russia, China, India, Australia, and the Pacific, Atlantic and Indian Oceans. The dividing lines visibly bend away from straight meridians to follow international borders. International borders on this map are approximate, not exact.

A globe centred on India showing GMT offsets for a number of countries — 0, +1, +2, +3, +3.5, +4, +4.5, +5, +5.5 (India), +6, +6.5, +7, +8, +9, +9.5, +10, +11, +12. The half-hour offsets show that not every zone is a whole number of hours.

1. On the map in Fig. 1.1 on page 8 — (a) Mark the hospital. (b) What is the meaning of the blue-coloured areas? (c) Which is farther away from the railway station — the school, the Nagar Panchayat or the public garden?
2. As a class activity, form groups of three or four. Each group draws a map of your school and some of the streets or roads leading to it, and a few neighbouring buildings. Compare all the maps and discuss.
3. Draw a simple map of a school playground, assuming it is a rectangle 40 m long and 30 m wide. Draw it precisely with your ruler on a scale of 1 cm = 10 m.
4. Now measure the diagonal of that rectangle. How many centimetres do you get? Using the scale, calculate the real length of the playground’s diagonal in metres.
5. Consider the map of the small city again. Identify the correct and incorrect statements: (a) The market is north of the hospital. (b) The museum is southeast of the bank. (c) The railway station is northwest of the hospital. (d) The lake is northwest of the apartment blocks.
6. Taking your school as the starting point, in which cardinal direction is your home? Discuss with your teacher and your parents.
7. Draw a rough map of your locality or village, including your home, school and a few other important landmarks. Show the cardinal directions and use a few of the symbols from Fig. 1.2.
8. Using chess notation, write down your move if you play black, and respond with the same move.
9. If the globe or atlas in your class has well-marked latitudes and longitudes, note down approximate values for the latitude and longitude of (1) Mumbai, (2) Kolkata, (3) Singapore, (4) Paris.
10. Two friends, one in Porbandar (Gujarat) and the other in Tinsukia (Assam), are speaking on the phone in the late afternoon. The one in Assam says the sun has set and it is now dark; the one in Gujarat is surprised and says it is still full daylight. Explain why. Then calculate the difference in local time between the two cities. (Hint: take the difference in longitude as 30°.)
11. Return to the two friends in Gujarat and Assam. Use this example to explain the difference between local time and standard time.

1. Returning to page 10 and to Fig. 5.2 in Chapter 5, taking the scale to be 2.5 cm = 500 km, calculate the real distance from the estuary of the Ganga river to the estuary of the Narmada river. (Hint: round off your measurement on the map to an easy number.)
2. Why is it 5:30 pm in India when it is 12 pm or noon in London?
3. Why do we need symbols and colours in the map?
4. Find out what you have in the eight directions from your home or school.
5. What is the difference between local time and standard time? Discuss in groups, with each group writing an answer in 100 to 150 words. Compare the answers.
6. Delhi’s and Bengaluru’s latitudes are 29°N and 13°N; their longitudes are almost the same, 77°E. How much will be the difference in local time between the two cities?
7. Mark the following statements as true or false; explain your answers with a sentence or two.
   • All parallels of latitude have the same length.
   • The length of a meridian of longitude is half of that of the Equator.
   • The South Pole has a latitude of 90°S.
   • In Assam, the local time and the IST are identical.
   • Lines separating the time zones are identical with meridians of longitude.
   • The Equator is also a parallel of latitude.
8. Solve the crossword below.