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

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?

Practice this conceptself-check · 3 quick reps

The same idea in a real exam question:

NDA · Apr 2022 · Q109Easy

Example 1 · Earth in Space, Maps and Coordinates · Maps and GPS

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?

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

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

The same idea in a real exam question:

NDA · Apr 2022 · Q110Easy

Example 2 · Earth in Space, Maps and Coordinates · Maps and GPS

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

\textbf{\text{not}}

correct?

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

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.

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