CDS Geography · Free notes
Earth in Space and Maps: CDS Geography
Earth in Space, Maps and Coordinates has 19 past-year questions in CDS General Knowledge, from 2016 (II) to 2026 (II): 3 EASY, 12 MODERATE and 4 HARD. Seven of them came in the two 2023 papers. Most ask one named fact: a planet's moons or clouds, the author of a theory, the meaning of an isoline. Seven are statement or matching items, where each statement has to be checked on its own, so learn the facts as true statements. The one real calculation is local time, and it needs a single rule: one degree of longitude is four minutes of time, with places to the east ahead.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
The Solar System
10 PYQsWho proposed which theory of how the Earth formed, the two families of planets, the planet facts CDS asks, and what syzygy, perihelion and aphelion mean.
Latitude, Longitude, Time and Maps
9 PYQsThe Earth's shape and spin, what latitude tells you about a place, how to turn a difference in longitude into a difference in time, and the isolines and diagrams of map work.
Formula & revision sheet
1 formulas · 7 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 7 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (4)
Theories of the origin of the Earth7 rows
| Theory | Proposed by |
|---|---|
| Gaseous (nebular) hypothesis | Immanuel Kant; revised by Laplace |
| Planetesimal hypothesis | Chamberlin and Moulton |
| Tidal hypothesis | James Jeans and Harold Jeffreys |
| Binary star hypothesis | H. N. RussellQ CDS 2026 (I): Kant gaseous, Russell binary star, Chamberlin planetesimal are all correctly matched. |
| Expanding universe (Big Bang) | Edwin Hubble showed the expansion |
| Tetrahedral hypothesis of continents and oceans | Lowthian GreenQ CDS 2026 (II): Lowthian Green, not Taylor, Wegener or Davis. |
| Continental drift | Alfred Wegener |
The two families of planets4 rows
| Family | Planets | Made of |
|---|---|---|
| Terrestrial (inner) | Mercury, Venus, Earth, Mars | Rock and metal; solid surfaceQ CDS 2020 (II): the four planets closest to the Sun are the terrestrial planets. |
| Giant or gas (outer) | Jupiter, Saturn, Uranus, Neptune | Hydrogen, helium and ices; no solid surfaceQ CDS 2023 (I): Mars is rocky, so any group of gas planets that includes Mars is wrong. |
| Dwarf planet | Pluto (since 2006) | Rock and ice; too small to clear its orbit |
| Asteroid belt | Between Mars and Jupiter | Rocky and metal fragments |
Planet facts CDS asks7 rows
| Planet | Fact to remember |
|---|---|
| Mercury | Smallest and least massive; almost no atmosphereQ CDS 2019 (I): Mercury has the least mass, less than Mars. |
| Venus | Hottest; thick clouds of sulphuric acid; no moonQ CDS 2022 (II): the yellowish clouds of Venus are sulphuric acid. |
| Mars | Red from iron oxide; two moons, Phobos and DeimosQ CDS 2023 (II): carbon dioxide is about 95 to 97% of the air of both Venus and Mars. |
| Jupiter | Largest planet; a gas giant with no solid surface |
| Saturn | Rings of ice and rocky dust; most known moonsQ CDS 2023 (II): Mercury has no atmosphere, Jupiter no land, Saturn's rings are ice and dust; Venus has no moons. |
| Uranus | Spins on its side |
| Neptune | Farthest planet from the Sun |
Syzygy, perihelion and aphelion5 rows
| Term | Meaning | When |
|---|---|---|
| Syzygy | Sun, Earth and Moon in a straight line | Every new moon and full moonQ CDS 2016 (II): 'syzygy conjunction occurs at the time of perihelion only' is the wrong statement. |
| Conjunction | Moon between the Sun and Earth | New moon |
| Opposition | Earth between the Sun and Moon | Full moon |
| Perihelion | Earth nearest the Sun | About 3 January |
| Aphelion | Earth farthest from the Sun | About 4 July |
Watch out for (6)
- Davis and Taylor are distractors for origin theories→ Theories of the origin of the Earth
- Planetesimal is Chamberlin, tidal is Jeans→ Theories of the origin of the Earth
- Mars is the last rocky planet→ The two families of planets
- Nearest is not hottest→ Planet facts CDS asks
- Moon counts change→ Planet facts CDS asks
- The Earth is nearest the Sun in January→ Syzygy, perihelion and aphelion
Reference tables (3)
The Earth's shape and rotation7 rows
| Fact | Value |
|---|---|
| Shape | Oblate spheroid, flattened at the poles |
| Circumference at the equator | About 40,000 km |
| Eratosthenes' two cities | Syene (Aswan) and AlexandriaQ CDS 2024 (II): Alexandria and Syene, not Troy or Thebes. |
| Direction of rotation | West to east |
| Angular velocity | 15° an hour, the same at every placeQ CDS 2024 (I): angular velocity is the same everywhere; linear velocity is greatest at the equator, least at the poles. |
| Linear velocity | About 1,670 km an hour at the equator; zero at the poles |
| Tilt of the axis | 23½° from the upright |
Latitude and what it tells you9 rows
| Line or place | Latitude or fact |
|---|---|
| Equator | 0° |
| Indira Point, Great Nicobar | About 6°45′ N, India's southernmost pointQ CDS 2017 (II): all three statements about latitude were true, including Indira Point at about 6°45′ N. |
| Panaji | About 15½° NQ CDS 2023 (II): Panaji is the closest of these four capitals to the equator. |
| Hyderabad | About 17½° N |
| Mumbai | About 19° N |
| Bhubaneswar | About 20° N |
| Tropic of Cancer | 23½° N |
| Arctic Circle | 66½° N |
| Parallels drawn every 1° | 89 in each hemisphere plus the equator: 179Q CDS 2025 (II): both statements true; 179 parallels, and a degree of latitude changes slightly in length. |
Isolines and diagrams10 rows
| Line or diagram | What it shows |
|---|---|
| Isotherm | Equal temperature |
| Isobar | Equal pressure |
| Isohyet | Equal rainfall |
| Isohel | Equal sunshine |
| Isonif | Equal snowfall |
| Isoneph | Equal cloudiness |
| Isohypse (contour) | Equal height above sea levelQ CDS 2023 (II): an isohypse joins equal height, not cloudiness. |
| Isobath | Equal depth of water |
| Scatter graph | Whether two sets of data are relatedQ CDS 2023 (I): population size against number of services needs a scatter graph. |
| Triangular graph | Three parts adding up to 100% |
Watch out for (8)
- Angular speed is the same, linear speed is not→ The Earth's shape and rotation
- Closest to the equator means lowest latitude→ Latitude and what it tells you
- The poles are not parallels→ Latitude and what it tells you
- IST is ahead, not behind→ Local time and longitude
- Opposite sides of Greenwich: add the longitudes→ Local time and longitude
- One time zone for all of India→ Local time and longitude
- Isoneph, not isohypse, is cloudiness→ Isolines and diagrams
- Two variables need a scatter graph→ Isolines and diagrams
PYQ weightage by concept
8 concepts · 19 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
8 concepts · 19 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Planet facts CDS asks | 5 | 26% |
| Theories of the origin of the Earth | 2 | 11% |
| The two families of planets | 2 | 11% |
| Syzygy, perihelion and aphelion | 1 | 5% |
| Concept | PYQs | Share |
|---|---|---|
| Latitude and what it tells you | 3 | 16% |
| The Earth's shape and rotation | 2 | 11% |
| Local time and longitude | 2 | 11% |
| Isolines and diagrams | 2 | 11% |
Test yourself on a real paper
Sit a past CDS paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.