11.4 World Geography

Why World Geography Matters for RRB Group D

World Geography questions in RRB Group D are fewer than Indian Geography — typically 1–2 per shift — and are highly predictable: continents, oceans, longest rivers, largest deserts, capitals, layers of the atmosphere, and basic Earth motions. Memorise a single fact table for each category and you cover most of the segment.

The Earth — Shape and Motions

Earth is an oblate spheroid (slightly flattened at the poles, bulging at the Equator). Its equatorial diameter (12,756 km) is greater than its polar diameter (12,714 km). It is the fifth largest planet and the fifth in distance from the Sun, after Mercury, Venus, Earth, and Mars — wait, that is wrong: it is the third from the Sun (Mercury, Venus, Earth). About 71% of the surface is water, 29% is land — hence the nickname "Water Planet".

Earth has two principal motions:

• Rotation — the spinning of Earth on its axis from west to east (anti-clockwise from above the North Pole). It takes 23 hours 56 minutes 4 seconds (sidereal day) for one rotation; the solar day is 24 hours. Rotation causes day and night and the Coriolis effect (deflection of winds and ocean currents to the right in the Northern Hemisphere, left in the Southern).
• Revolution — Earth's orbit around the Sun, taking 365 days 5 hours 48 minutes 46 seconds. This is the basis of the year and the leap year rule (every 4 years, except century years not divisible by 400). Revolution, combined with the 23.5° tilt of the axis, causes the seasons, the varying length of day and night, and the four key positions: Summer Solstice (21–22 June, longest day in Northern Hemisphere), Winter Solstice (21–22 December, shortest day in NH), Vernal Equinox (20–21 March), and Autumnal Equinox (22–23 September).

Latitudes and Longitudes

Latitudes (Parallels) — imaginary lines parallel to the Equator, measuring distance north/south, from 0° at the Equator to 90° N (North Pole) and 90° S (South Pole). The Equator (0°) is the longest latitude (~40,075 km) and the only great circle among the parallels. Important parallels: Tropic of Cancer (23°30' N), Tropic of Capricorn (23°30' S), Arctic Circle (66°30' N), Antarctic Circle (66°30' S). Latitudes get shorter toward the poles.

Longitudes (Meridians) — imaginary lines running from the North Pole to the South Pole, measuring distance east/west from the Prime Meridian (0°), which passes through Greenwich near London. They meet at the poles, so they are widest at the Equator (~111 km per degree) and zero at the poles. There are 360° of longitude, divided into 24 time zones of 15° each (1 hour per 15°). The International Date Line roughly follows the 180° longitude; crossing it eastward you subtract a day, westward you add a day.

Time Zones — Earth is divided into 24 standard time zones. IST (Indian Standard Time) is UTC+5:30, based on the 82°30' E meridian through Mirzapur. Countries with multiple time zones: Russia (11), USA (6 main, 9 including territories), Canada (6), Australia (3 main). A single time zone country: India, China, Bangladesh.

Layers of the Atmosphere

From Earth's surface outward:

1. Troposphere (0–12 km): contains most weather; temperature decreases with height (lapse rate ~6.5°C/km); the Tropopause caps it.
2. Stratosphere (12–50 km): contains the ozone layer (15–35 km) that absorbs UV radiation; temperature increases with height; ideal for jet flights.
3. Mesosphere (50–80 km): where most meteors burn up; coldest layer (-90°C).
4. Thermosphere / Ionosphere (80–600 km): contains ions reflecting radio waves; auroras (Northern and Southern Lights) occur here; ISS orbits here (~400 km).
5. Exosphere (>600 km): merges with outer space; satellites in high orbits.

Continents and Oceans

Oceans (in descending order of size):

1. Pacific Ocean — largest and deepest; contains the Mariana Trench (deepest point, Challenger Deep, ~11,034 m); separates Asia/Australia from the Americas; Ring of Fire around it has the most active volcanoes and earthquakes.
2. Atlantic Ocean — second largest; "S" shaped; busiest for trade; separates the Americas from Europe and Africa; the Mid-Atlantic Ridge runs along its middle.
3. Indian Ocean — third largest; the warmest ocean; borders India, Africa, Australia, and SE Asia; the only ocean named after a country.
4. Southern (Antarctic) Ocean — fourth largest; surrounds Antarctica; cold circumpolar current; recognised as a separate ocean by the IHO in 2000.
5. Arctic Ocean — smallest and shallowest; mostly covered by ice; located around the North Pole.

Major Landforms

Mountains — three types: Fold (Himalayas, Andes, Alps, Rockies — formed by compression of sediments between colliding plates), Block (Fault-block) (Vindhyas, Black Forest, Sierra Nevada — formed by faulting and uplifting), Volcanic (Andes, Rockies partly; Mauna Kea; Kilimanjaro). The Andes is the longest mountain range on land (~7,000 km), and the Himalayas the highest.

Plateaus — extensive flat-topped elevated areas: Tibetan Plateau (the "Roof of the World", highest, ~4,500 m), Iranian Plateau, Anatolian Plateau (Turkey), Deccan Plateau (India), Colorado Plateau (USA), Central Siberian Plateau.

Plains — flat or gently rolling areas, often river valleys: Indo-Gangetic Plain, North China Plain, Great Plains (USA), Plains of Eastern Europe, Amazon Basin.

Deserts — large arid areas; the Sahara (Africa, ~9 million sq km — largest hot desert), the Gobi (Mongolia–China — largest cold desert outside the polar regions), the Kalahari (southern Africa), the Atacama (Chile — driest), the Arabian Desert, the Thar (India), the Great Basin (USA), and the polar deserts — the Antarctic Desert (largest desert overall by area, ~14 million sq km).

World Rivers

Climatic Regions

Earth's climate is classified by the Köppen system into five main groups:

• A — Tropical (equatorial): rainforest, monsoon, savanna; found near the Equator (Amazon, Congo, Indonesia, parts of India).
• B — Dry (arid & semi-arid): deserts (BW) and steppes (BS); Sahara, Atacama, Gobi, Thar, Australian Outback.
• C — Temperate (mid-latitude): Mediterranean (Cs), humid subtropical (Cf), marine west coast (Cf); much of Europe, eastern USA, eastern China, coastal California.
• D — Continental (cold): hot summer continental and subarctic; Russia, Canada, interior north-east USA.
• E — Polar: tundra (ET) and ice cap (EF); Arctic and Antarctic, Greenland.

India's climate is broadly Tropical Monsoon (Am) with Humid Subtropical (Cwa) in the north and Tropical Wet-Dry (Aw) over much of the peninsula.

Important Lines and Boundaries

• Equator (0°): passes through 13 countries including Ecuador, Colombia, Brazil, Kenya, Uganda, Indonesia.
• Prime Meridian (0°): passes through Greenwich; crosses UK, France, Spain, Algeria, Mali, Burkina Faso, Togo, Ghana.
• International Date Line: ~180°; zig-zags to keep countries on the same day.
• McMahon Line: India–China boundary in the east.
• Radcliffe Line: India–Pakistan boundary (1947).
• Durand Line: Pakistan–Afghanistan boundary (1893).
• 38th Parallel: divides North and South Korea.
• 49th Parallel: USA–Canada boundary (western part).

Exam Scenario Alert

RRB Group D world geography questions tend to be: "Which is the largest continent?" (Asia), "Which is the deepest ocean trench?" (Mariana Trench, in the Pacific), "Which is the longest river in the world?" (Nile), "Which layer of the atmosphere contains the ozone layer?" (Stratosphere), "Which is the smallest continent?" (Australia). Memorise a one-line fact for each category.