NDA Geography · Free notes
Earth in Space, Maps and Coordinates — NDA Geography
This chapter is the 'how the Earth sits in space and how we pin a point on it' chapter — 24 PYQs across 2017–2026, spatial and conceptual rather than recall-heavy. Almost every question rewards a clear mental picture: a spinning, tilted, slightly-squashed ball going round the Sun, wrapped in a grid of latitude and longitude, sliced into 24 time zones. Get those pictures right and the marks follow without memorising long lists. The chapter teaches in a logical arc, from the planet's own motions outward to the wider Solar System: (1) Earth's shape, rotation and motion — oblate spheroid, day/night from rotation, seasons from revolution + tilt, linear velocity fastest at the Equator; (2) latitude, longitude and the geographical grid — parallels vs meridians, the Equator as the longest parallel, great circles; (3) time zones and the International Date Line — the 15-degrees-per-hour rule and the date change at 180 degrees; (4) maps and GPS — what you need to locate a place and what GPS actually does; (5) planets and the Solar System — order, terrestrial vs giant planets, density ranking (Earth densest). 5 subtopics, ~21 concepts, every PYQ tagged. The 'Shape, Rotation and Motion' subtopic is the largest and carries the trickiest reasoning questions.
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
Earth's Shape, Rotation and Motion
8 PYQsThe Earth is a slightly squashed ball (an oblate spheroid) that spins on a tilted axis once a day and circles the Sun once a year — its rotation gives day and night, its revolution plus tilt gives the seasons.
Latitude, Longitude and the Geographical Grid
6 PYQsLatitude and longitude form the grid of imaginary lines that lets us name any point on Earth — parallels run east-west and shrink toward the poles, meridians run pole to pole and are all equal in length.
Time Zones and the International Date Line
4 PYQsThe Earth turns 360 degrees in 24 hours, so every 15 degrees of longitude equals one hour — going east adds time, going west subtracts it, and the date changes by a day at the International Date Line near 180 degrees.
Maps and GPS
2 PYQsA map needs a place's latitude and longitude to pin it down, while the Global Positioning System uses a network of orbiting satellites and triangulation to give your latitude, longitude and altitude.
Planets and the Solar System
4 PYQsEight planets orbit the Sun — the four small rocky terrestrial planets inside the asteroid belt and the four giant planets outside it — and the universe itself is explained by the Big Bang theory.
Formula & revision sheet
0 formulas · 2 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 2 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Watch out for (7)
- Polar diameter is NOT greater→ The shape of the Earth — oblate spheroid
- Bulge = rotation, not revolution→ The shape of the Earth — oblate spheroid
- Tides are not caused by rotation→ Rotation — day, night and its effects
- Angular speed is equal — LINEAR speed is not→ Linear velocity of rotation is fastest at the Equator
- Tilt limits the overhead Sun to 23.5 degrees→ Where the Sun can be overhead — the Tropics
- Which Indian states NEVER get a perpendicular Sun — go by the Tropic→ Where the Sun can be overhead — the Tropics
- Don't pick an equinox for the shortest day→ Solstices, equinoxes and day length
Watch out for (3)
- Longest latitude = Equator, not 90 degrees→ The Equator is the longest parallel of latitude
- Only the Equator and full meridians are great circles→ Equal meridians, unequal parallels, and great circles
- Read the exact zone names before ordering→ Latitudinal heat zones and their extent
Watch out for (3)
- East adds, West subtracts→ The 15-degrees-per-hour rule and the direction of time
- The IDL is in the Pacific, not the Atlantic→ The International Date Line
- East of the line is BEHIND, not ahead→ The International Date Line
Reference tables (1)
What GPS is and what it does4 rows
| GPS feature | Correct? | Detail |
|---|---|---|
| Based on a network of orbiting satellites | TRUE | A constellation of satellites circling above the Earth |
| Uses the system of triangulation | TRUE | Distances from several satellites are combined to fix the position |
| Gives latitude, longitude and altitude | TRUE | GPS receivers report full 3-D position |
| For military operations ONLY | FALSE | Widely civilian — navigation, mapping, surveying, phones NDA 2022 — this is the 'NOT correct' statement: GPS is NOT exclusively military. |
Watch out for (2)
- Altitude is not needed to LOCATE a place→ What you need to locate a place on a map
- GPS is not military-only→ What GPS is and what it does
Reference tables (1)
Theories of the origin of the universe and Solar System4 rows
| Theory / hypothesis | Explains | Idea |
|---|---|---|
| Big Bang theory | Origin of the universe | Universe expanded from a hot, dense single point NDA 2019 — the universe's origin is the Big Bang. |
| Nebular hypothesis | Origin of the Solar System | Sun and planets formed from a spinning gas-dust cloud (nebula) |
| Planetesimal hypothesis | Origin of the Solar System | Planets built up from small bodies (planetesimals) |
| Binary / tidal theory | Origin of the Solar System | A passing star pulled matter off the Sun |
Watch out for (4)
- Big Bang = universe, Nebular = Solar System→ Theories of the origin of the universe and Solar System
- Terrestrial planets have HIGHER density, not lower→ Planet order: terrestrial vs giant planets
- Terrestrial planets lie INSIDE the asteroid belt→ Planet order: terrestrial vs giant planets
- Densest is EARTH, not Jupiter→ Density ranking — Earth is the densest planet
PYQ weightage by concept
20 concepts · 24 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
20 concepts · 24 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| The shape of the Earth — oblate spheroid | 2 | 8% |
| Rotation — day, night and its effects | 1 | 4% |
| Why we do not feel the Earth spin | 1 | 4% |
| Linear velocity of rotation is fastest at the Equator | 1 | 4% |
| Where the Sun can be overhead — the Tropics | 1 | 4% |
| Which places the Equator passes through | 1 | 4% |
| Solstices, equinoxes and day length | 1 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| The Equator is the longest parallel of latitude | 2 | 8% |
| Latitude and longitude — the geographical grid | 1 | 4% |
| Equal meridians, unequal parallels, and great circles | 1 | 4% |
| How meridian spacing changes — and counting the lines | 1 | 4% |
| Latitudinal heat zones and their extent | 1 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| The International Date Line | 2 | 8% |
| The 15-degrees-per-hour rule and the direction of time | 1 | 4% |
| Finding a place's clock time from GMT | 1 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| What you need to locate a place on a map | 1 | 4% |
| What GPS is and what it does | 1 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| Density ranking — Earth is the densest planet | 2 | 8% |
| Theories of the origin of the universe and Solar System | 1 | 4% |
| Planet order: terrestrial vs giant planets | 1 | 4% |
Test yourself on Earth in Space, Maps and Coordinates
10 past NDA questions from this chapter, timed at 10 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.