NDA Geography · Earth in Space, Maps and Coordinates

Maps and GPS

A 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.

All Earth in Space, Maps and Coordinates notes NDA Geography strategy

Why this matters

2 PYQs, both EASY. Two facts cover them: to LOCATE a place on a map you need both its latitude and its longitude (altitude is extra, not required), and GPS is a satellite-triangulation system that gives 3-D position for civilian AND military use — it is NOT military-only.

Concept 1 of 2

What you need to locate a place on a map

Intuition

To pin a single point on a flat map you need TWO coordinates: how far north or south (latitude) and how far east or west (longitude). One alone is not enough — latitude alone gives you a whole east-west line, longitude alone a whole north-south line. Altitude (height) tells you nothing about WHERE on the map a place is, only how high it stands.

Definition

To locate a place on a map you need BOTH its latitude and its longitude — the pair fixes the point where the two lines cross.
Latitude alone is insufficient (it names a full east-west parallel); longitude alone is insufficient (it names a full north-south meridian).
Altitude is NOT required to locate a place on a map — altitude is the height above sea level, a vertical measure, not a horizontal position.

Worked example

You hear of an unfamiliar town on the news and want to find it on a map. What is the minimum information you need?

A map position is a horizontal point, fixed by two coordinates.
Those are latitude (north-south) and longitude (east-west).
Altitude would tell you the height, not the map position.

Answer:Both the latitude and the longitude of the place.

Practice this conceptself-check · 3 quick reps

Try it yourself

Is knowing only a place's latitude enough to locate it on a map?

Practice — Level 1 (3 reps)

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

1.
Minimum coordinates to locate a place on a map?
2.
Is altitude needed to locate a place on a map?
3.
Latitude alone fixes what?

From the bank · past-year question

Example 1Earth in Space, Maps and CoordinatesEASY

While watching news, you hear about a place, of which you had never heard earlier. You want to know more about the place and you want to locate it on the map. Which of the following is/are required for you to be able to locate the place on the map?

[Q109 · Apr · 2022]

Altitude is not needed to LOCATE a place

A choice offers 'latitude, longitude AND altitude'. Altitude is a vertical height — it does not help fix the horizontal map position. The correct minimum is just latitude and longitude.

Concept 2 of 2

What GPS is and what it does

Intuition

The Global Positioning System is a ring of satellites that lets a receiver work out exactly where it is. The receiver listens to several satellites and uses triangulation to compute its latitude, longitude AND altitude. Crucially, although GPS began as a military system, it is now used by everyone — phones, cars, ships, surveyors — so it is NOT for the military only.

Definition

GPS in four facts. The NDA tests the ONE statement that is NOT correct (it is military-only):

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.

Practice this conceptself-check · 4 quick reps

Try it yourself

Which statement about GPS is NOT correct: (a) based on satellites, (b) uses triangulation, (c) gives latitude/longitude/altitude, (d) for military use only?

Practice — Level 1 (4 reps)

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

1.
GPS relies on a network of what?
2.
What technique does GPS use to fix position?
3.
Which three values does a GPS receiver give?
4.
Is GPS for military use only?

From the bank · past-year question

Example 2Earth in Space, Maps and CoordinatesEASY

Which one of the following statements with respect to Global Positioning System (GPS) is

\textbf{\text{not}}

correct?

[Q110 · Apr · 2022]

GPS is not military-only

The 'which statement is NOT correct' twist hides the falsehood that GPS serves the military exclusively. GPS is everywhere in civilian life — that statement is the wrong one to pick as the answer.

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.

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

Drill every past-year question on this subtopic

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

Drill the 2 questions