NDA Geography · Earth in Space, Maps and Coordinates
Latitude, Longitude and the Geographical Grid
Latitude 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.
Why this matters
6 PYQs, mostly EASY to MODERATE 'which is/are correct' and 'arrange in order' questions. Master four facts: parallels run east-west and meridians run north-south, the Equator is the longest parallel (and a great circle), meridians all have equal length while parallels shrink toward the poles, and a great circle is any circle whose plane passes through the Earth's centre.
Concept 1 of 5: Latitude and longitude — the geographical grid
Two families of lines wrap the globe. Parallels of latitude run east to west (like the rungs of a ladder) and measure how far north or south of the Equator you are. Meridians of longitude run north to south, from pole to pole, and measure how far east or west of the Prime Meridian you are. Together they form the geographical grid, so any place is fixed by a (latitude, longitude) pair.
Definition
- Latitude — angular distance north or south of the Equator (0 deg to 90 deg). Its lines, the parallels, run east to west around the globe and are parallel to one another.
- Longitude — angular distance east or west of the Prime Meridian (0 deg to 180 deg). Its lines, the meridians, run north to south from the North Pole to the South Pole.
- The crossing of the two families is the geographical grid; a place is located by its latitude AND longitude together.
- Number of meridians (longitudes) is greater than the number of parallels (latitudes) in the usual convention: 360 meridians (one per degree of longitude, 0–180 each side) versus 181 parallels (90 each side plus the Equator).
Worked example
A grid book says: 'Lines running east-west mark latitude; lines running north-south from pole to pole mark longitude.' Are both statements correct?
Practice this conceptself-check · 3 quick reps
The same idea in a real exam question:
NDA · Sep 2023 · Q80Easy
Example 1 · Earth in Space, Maps and Coordinates · Latitude, Longitude and Geographical Grid
A geographical grid has:
1. Lines that run east to west around the globe to mark latitude
2. Lines that run north to south from north pole to south pole indicate longitude
Which of the statements given above is/are correct?
Concept 2 of 5: The Equator is the longest parallel of latitude
Parallels are circles around the globe, and they get smaller the closer you go to a pole. The biggest of all is the one around the middle — the Equator (0 deg). The Tropic of Cancer, Arctic Circle and the rest are all shorter, and at the poles a 'parallel' shrinks to a single point. So the longest latitude line is always the Equator.
Definition
- Parallels of latitude shrink toward the poles — they are largest at the Equator and become a point at 90 deg (the poles).
- The Equator (0 deg latitude) is the longest parallel and the only parallel that is a great circle.
- So when asked for the 'longest latitude' or 'longest parallel', the answer is the Equator, NOT 23.5 deg or 66.5 deg.
- 90 deg latitude is a single point (a pole), which is the SHORTEST possible parallel.
Worked example
Order these parallels from longest to shortest: Arctic Circle (66.5 deg N), Tropic of Cancer (23.5 deg N), Equator (0 deg).
Practice this conceptself-check · 3 quick reps
The same idea in a real exam question:
NDA · Sep 2021 · Q77Easy
Example 2 · Earth in Space, Maps and Coordinates · Latitude, Longitude and Geographical Grid
Which one of the following is the longest parallel of latitude?
Longest latitude = Equator, not 90 degrees
A 'longest latitude' question may list 90 deg as a tempting big-number choice. But 90 deg is a pole — a single point, the SHORTEST. The longest is 0 deg, the Equator.
Concept 3 of 5: Equal meridians, unequal parallels, and great circles
All meridians of longitude are the same length — each is a half-circle from pole to pole — and the gap between two meridians is widest at the Equator and shrinks to zero at the poles. Parallels are unequal (shrinking poleward). A great circle is any circle on the globe whose plane passes through the Earth's centre — the Equator and every full meridian-pair are great circles, but the smaller parallels (Tropics, Arctic Circle) are NOT.
Definition
- Distance between meridians (longitudes) is maximum at the Equator and becomes zero at the poles (the meridians meet there).
- Parallels are unequal in length (shrink poleward); meridians are all equal in length.
- A Great Circle = a circle whose plane passes through the centre of the Earth, dividing it into two equal halves. It is the shortest route between two points on the globe.
- The Equator is a great circle; every meridian (paired with its opposite to make a full circle) is part of a great circle.
- The Tropic of Cancer, Arctic Circle and other parallels are NOT great circles (their planes do not pass through the centre) — they are small circles.
Worked example
Of the Prime Meridian, the Tropic of Cancer and the Equator, which are great circles?
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
NDA · Apr 2025 · Q86Moderate
Example 3 · Earth in Space, Maps and Coordinates · Latitude, Longitude and Geographical Grid
Consider the following lines of Longitude and Latitude :
1. Prime Meridian
2. Tropic of Cancer
3. Equator
Which of the above lines is/are a Great Circle?
Only the Equator and full meridians are great circles
Among latitude lines, ONLY the Equator is a great circle. The Tropics, Arctic and Antarctic Circles are small circles. Every full meridian, however, lies on a great circle. So 'Prime Meridian + Equator' is the classic correct pair.
Concept 4 of 5: How meridian spacing changes — and counting the lines
Three facts get bundled into multi-statement questions: the gap between meridians is zero at the poles (where they meet), maximum at the Equator, and there are more longitudes than latitudes in the standard count. All three are true together, so 'all of the above' is the usual answer.
Definition
All three of these statements are correct:
- The distance between two longitudes (meridians) becomes zero at the North and South Poles — the meridians converge there.
- The distance between two longitudes is maximum at the Equator.
- The number of longitudes is greater than the number of latitudes (360 meridians at 1 deg spacing vs 181 parallels including the Equator).
Worked example
True or false: 'There are more lines of longitude than lines of latitude on the standard grid.'
Practice this concept3 quick reps
The same idea in a real exam question:
NDA · Apr 2023 · Q93Moderate
Example 4 · Earth in Space, Maps and Coordinates · Latitude, Longitude and Geographical Grid
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
Concept 5 of 5: Latitudinal heat zones and their extent
Latitude bands group into climatic/heat zones, and the NDA asks you to ORDER them by how wide a band of latitude each covers. From the Equator outward: the equatorial/tropical belt near the middle, the mid-latitude (temperate) belt, then the subarctic/polar belts. Each zone spans a different number of degrees of latitude, so 'arrange by latitudinal extent' is really 'arrange by band width'.
Definition
- Latitudinal (heat) zones are bands of latitude with similar Sun-angle and climate: the Torrid/Tropical zone (0–23.5 deg), the Temperate/mid-latitude zone (23.5–66.5 deg), and the Frigid/polar (incl. subarctic) zone (66.5–90 deg).
- Questions ask you to arrange zones by their latitudinal extent (the width of the latitude band each occupies), ascending or descending.
- The narrow equatorial belt is small; the mid-latitude/temperate belt is the widest band of the three main zones.
- Read the question's exact zone names and order them by band width — the trap is the ordering, not the geography.
Worked example
Arrange by latitudinal extent (narrowest first): a narrow equatorial belt, the wide mid-latitude belt, the subarctic belt.
Practice this concept3 quick reps
The same idea in a real exam question:
NDA · Sep 2025 · Q111Moderate
Example 5 · Earth in Space, Maps and Coordinates · Latitude, Longitude and Geographical Grid
Arrange the following zones in ascending order in terms of their latitudinal extent on the Earth surface :
1. Equatorial zone
2. Midlatitude zone
3. Subarctic zone
4. Tropical zone
Select the answer using the code given below :
Read the exact zone names before ordering
These 'arrange the zones' questions give a fixed coded order (e.g. 1-4-2-3). The mistake is mis-ordering the band widths, not the geography — line up each named zone with its degree-span and sort carefully.
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 (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
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