Chapter 1: Locating Places on the Earth (Geography)

Method: measure the straight-line distance on the map between the mouth of the Narmada (Gulf of Khambhat, on the west coast) and the mouth of the Ganga (near the Bay of Bengal, in West Bengal), then use the scale.

Scale: 2.5 cm = 500 km, so 1 cm = 200 km.

On the map the distance is about 8.5 cm (rounding off). Real distance ≈ $8.5\times 200=$ about 1,700 km.

(Your measurement may differ slightly depending on the map; the true straight-line distance is roughly 1,700–1,800 km.)

About 8.5 cm on the map × 200 km per cm ≈ 1,700 km.

London lies on the Prime Meridian (0°), while Indian Standard Time is based on the 82°30′E meridian. The Earth rotates from west to east, so places to the east see the Sun earlier and are ahead in time. Each 1° of longitude makes a difference of 4 minutes:

$$82.5\times 4\text{min}=330\text{min}=5\text{h}30\text{min}$$

So when it is noon in London, it is 5:30 pm in India.

India's standard meridian (82°30′E) is 82.5° east of London, and 82.5 × 4 min = 5 h 30 min, so India is 5½ hours ahead.

• A map is small, so we cannot draw every house, road, river or temple as it really looks or write all the names; symbols stand for them in little space (e.g. a cross for a hospital, a line for a railway).
• Colours show different features at a glance: blue for water, green for plains and forests, yellow or brown for plateaus and mountains.
• Symbols and colours are understood by everyone (they are standard) and explained in the map's key or legend, so maps can be read easily anywhere.

Symbols and colours save space, show features clearly at a glance, and are standard, so anyone can read the map using its key.

Stand at your gate and use the Sun (it rises in the east) or a compass to find north. Then note what lies in each of the eight directions. Example for a school:

(Make your own table for your home or school.)

Find north with a compass or the Sun, then list what lies to the N, NE, E, SE, S, SW, W and NW (make your own table).

Local time is the time of a place worked out from the position of the Sun in its own sky: it is 12 noon when the Sun is highest overhead at that place. Since the Earth rotates, the Sun is highest at different moments for places on different longitudes, so local time changes by 4 minutes for every degree of longitude. Two places only a few hundred kilometres apart from east to west would have different local times.

If every town used its own local time, timetables for trains, flights, offices and schools would be very confusing. So a country chooses one meridian and uses its local time everywhere: this is the standard time. In India, the local time of the 82°30′E meridian (passing near Mirzapur, Uttar Pradesh) is used throughout the country as Indian Standard Time (IST), which is 5 hours 30 minutes ahead of Greenwich Mean Time. Large countries such as Russia or the USA have several standard time zones.

Local time depends on the Sun's position at each place (changing 4 min per degree of longitude); standard time is the local time of one chosen meridian used across a country (IST, at 82°30′E) so that everyone follows the same clock.

Local time depends only on longitude, not latitude. Both cities are on almost the same longitude (77°E), so the difference in local time is almost zero: they have the same local time.

Almost none: local time depends on longitude, and both are at about 77°E.

(a) False. The Equator is the longest parallel; parallels become smaller towards the poles, which are just points.

(b) True. A meridian runs from the North Pole to the South Pole, which is half way round the Earth, so it is half the length of the Equator (which goes all the way round).

(c) True.

(d) False. Assam is at about 92°E, about 10° east of the IST meridian (82°30′E), so its local time is about 40 minutes ahead of IST; the Sun rises much earlier there.

(e) False. Time-zone boundaries mostly follow meridians but bend to follow country and state borders, so they are zig-zag, not straight meridians.

(f) True. It is the 0° parallel of latitude, the longest one.

(a) F (b) T (c) T (d) F, Assam is about 40 min ahead of IST (e) F, the boundaries bend along borders (f) T

Across: SCALE, GLOBE, EQUATOR, GREENWICH, MAP, LATITUDE. Down: LONGITUDE, COORDINATES, GRID, IST, NORTH POLE, IDL.