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NDA Geography · World and Human Geography

World Coordinates, Time and Place

How latitude and longitude fix a place on the globe, how longitude controls local time (GMT offsets, the Prime Meridian) and what happens when you cross the International Date Line.

All World and Human Geography notesNDA Geography strategy

Why this matters

4 PYQs, all MODERATE. Two are pure recall (which capital is northernmost, which African country the Prime Meridian misses), but two test a RULE: time changes with longitude (1 hour per 15°), so the country farthest east of Greenwich has the biggest time difference, and crossing the International Date Line east means you set the clock back a day. Learn the rule and you don't have to memorise every case.

Concept 1 of 3

Latitude, longitude and locating a place

Intuition

Every place on Earth is fixed by two numbers. LATITUDE measures how far north or south of the Equator you are (0° at the Equator, 90° at the poles) — bigger latitude means closer to a pole. LONGITUDE measures how far east or west of the Prime Meridian (0°) you are. So to ask 'which place is northernmost', you simply compare latitudes: the one nearest the North Pole wins.

Definition

  • Latitude — angular distance north or south of the Equator (0° to 90°). Higher north latitude = farther north.
  • Longitude — angular distance east or west of the Prime Meridian (0° to 180°).
  • 'Northernmost' = the location with the highest northern latitude. Among South-Asian capitals, New Delhi (~28.6° N) lies north of Kathmandu, Thimphu and Dhaka.

Worked example

Of four South-Asian capitals — New Delhi, Kathmandu, Thimphu, Dhaka — which is the northernmost?
  1. 'Northernmost' means the highest northern latitude.
  2. Kathmandu, Thimphu and Dhaka all sit in the Himalayan/Gangetic belt around 27°–28° N.
  3. New Delhi lies at about 28.6° N, just north of the others.
Answer:New Delhi.
Practice this conceptself-check · 3 quick reps

Try it yourself

A place at 0° latitude lies on which line?

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

  1. 1.
    Latitude is measured north/south of which line?
  2. 2.
    Longitude is measured east/west of which line?
  3. 3.
    'Northernmost' means the highest what?

From the bank · past-year question

Example 1World and Human GeographyMODERATE
Which one among the following is the northernmost geographical location?

[Q92 · Apr · 2023]

Concept 2 of 3

Longitude, GMT offsets and the Prime Meridian

Intuition

The Earth turns 360° in 24 hours, so it sweeps 15° of longitude every hour — that is why local time changes as you move east or west. Greenwich (0° longitude) sets Greenwich Mean Time; a place to the east is AHEAD of GMT, a place to the west is BEHIND. So among a group of countries, the one whose standard meridian is farthest EAST of Greenwich has the largest positive time difference from GMT. The Prime Meridian itself (0°) is a geography fact: it runs through a fixed string of countries, so a question can ask which listed country it does NOT cross.

Definition

  • The Earth rotates 15° of longitude per hour (360° in 24 hours), so 1° ≈ 4 minutes of time.
  • Places east of Greenwich are ahead of GMT; places west are behind.
  • Among India, Nepal, Sri Lanka and Bhutan, Bhutan lies farthest east, so it has the maximum time difference from GMT.
  • The Prime Meridian (0°) crosses several African countries — including Algeria, Mali and Ghana — but NOT Morocco.

Worked example

Of India, Nepal, Sri Lanka and Bhutan, which has the maximum time difference from GMT?
  1. Time difference from GMT grows the farther east a country's standard meridian lies.
  2. Of the four, Bhutan is the easternmost.
  3. So Bhutan is the most hours ahead of GMT.
Answer:Bhutan.
Practice this conceptself-check · 3 quick reps

Try it yourself

If you move 30° of longitude east, by how much does local time change?

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

  1. 1.
    How many degrees of longitude does the Earth turn per hour?
  2. 2.
    Is a place east of Greenwich ahead of or behind GMT?
  3. 3.
    Which of Morocco, Algeria, Mali, Ghana does the Prime Meridian NOT cross?

From the bank · past-year question

Example 2World and Human GeographyMODERATE
Which one of the following countries has the maximum time difference from Greenwich Mean Time (GMT)?

[Q67 · Sep · 2021]

East = ahead, but the DATE line is the opposite

Moving east of Greenwich puts you AHEAD in time — but crossing the International Date Line going east makes you set the clock BACK a day. Keep the two ideas separate (see the next concept).
Drill 1 more on longitude, gmt offsets and the prime meridian

Concept 3 of 3

The International Date Line

Intuition

The International Date Line (IDL) runs roughly along the 180° meridian, opposite the Prime Meridian. It is where the calendar date changes. The rule reverses what you expect from time: when you fly EAST across the IDL you SUBTRACT a day (you 'lose' 24 hours, i.e. repeat the date); flying WEST across it you ADD a day. The NDA tests exactly this 'east across the IDL = lose 24 hours' fact.

Definition

  • The International Date Line follows about the 180° meridian and is where the calendar date changes.
  • Crossing the IDL travelling EAST → set the date back one day (you 'lose' 24 hours).
  • Crossing the IDL travelling WEST → set the date forward one day (you 'gain' 24 hours).

Worked example

What happens to your calendar date when you fly WEST across the International Date Line?
  1. The IDL is where the date changes.
  2. Going east across it subtracts a day; going west does the opposite.
  3. So crossing it westward you advance the date by one day.
Answer:You gain a day (set the date forward 24 hours).
Practice this conceptself-check · 3 quick reps

Try it yourself

Flying EAST across the International Date Line, do you gain or lose a day?

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

  1. 1.
    The International Date Line lies near which meridian?
  2. 2.
    Flying east across the IDL: gain or lose a day?
  3. 3.
    Flying west across the IDL: gain or lose a day?

From the bank · past-year question

Example 3World and Human GeographyMODERATE
What will happen if you are flying east across the International Date Line?

[Q94 · Sep · 2022]

East across the date line LOSES 24 hours

Intuition says 'east = ahead = gain', but for the International Date Line it is the opposite: flying EAST across it you lose 24 hours (set the date back). West across it you gain a day.

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Watch out for (2)

Mastery check — 1 interleaved questions

Try each one before clicking. Questions are interleaved across the concepts above, not grouped — interleaving sharpens transfer.

Example 1World and Human GeographyMODERATE
The Prime Meridian does not pass through which one of the following African countries?

[Q95 · Sep · 2022]

Drill every past-year question on this subtopic

4 questions from the bank — paginated, with cart and Word-export support.

Drill the 4 questions