ATPL General Navigation

Latitude & Longitude

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ATPL General Navigation35 min

Latitude & Longitude

How every position on Earth is defined

Every position on Earth can be described using two angular coordinates: latitude and longitude. Latitude tells us how far north or south a position is from the Equator. Longitude tells us how far east or west it is from the Prime Meridian.

Learning objectives

By the end of this chapter, you should be able to:

  • 01Define latitude and longitude
  • 02Identify the Equator and Prime Meridian
  • 03Recognise the Northern, Southern, Eastern and Western Hemispheres
  • 04Read and write geographical coordinates
  • 05Understand degrees, minutes and seconds
  • 06Identify a position from given coordinates
  • 07Determine whether two positions are north, south, east or west of each other
01Section 1

The Earth Reference System

Before any position can be measured we need fixed references. Two of them do all the work: the Equator and the Prime Meridian.

The Earth rotates about an axis that passes through the North and South Poles. The Equator is the great circle exactly halfway between the poles, at right angles to that axis. The Prime Meridian is the semi-great-circle running from pole to pole through Greenwich. Select any label on the diagram to highlight it.

Interactive educational diagram

Earth reference system — orthographic schematic

Select any label (or tap a feature on the globe) to highlight it and read its definition. Use Tab and Enter for keyboard control.

Schematic globe showing the Earth reference systemA circular Earth viewed from the plane of the Equator. The Equator is a horizontal red line through the centre, the Prime Meridian a vertical green line, the North Pole is at the top and the South Pole at the bottom, joined by the dashed axis of rotation. Labels around the globe name each feature and the four hemispheres.North Pole 90° NSouth Pole 90° SEquator 0°Prime Meridian 000°Earth's centreAxis of rotationNorthern HemisphereSouthern HemisphereEastern HemisphereWestern Hemisphere

Reference elements

Information

Nothing selected

Choose an element above to see how it fits into the Earth reference system.

02Section 2

Latitude — North or South

Latitude is the angular distance of a position north or south of the Equator. It is measured along a meridian from the Equator to the position.

Interactive educational diagram

Latitude as an angle at the Earth's centre

Move the latitude slider (or use the arrow keys) to see position P, its parallel and the centre angle φ change together.

Cross-section of the Earth through a meridianEducational diagram: a circular cross-section of the Earth. One radius runs horizontally from the centre to the Equator, a second radius runs to position P at 30° N. The angle phi between the two radii, measured at the centre of the Earth, is the latitude. The parallel of latitude through P is drawn as a horizontal chord.Equator 0°φcentreP — 30° N90° N — North Pole90° S — South Pole
30° N
-9090

Coordinate

30° N

30° north of the Equator

Hemisphere

Northern Hemisphere (suffix N)

The parallel through P is a small circle — only the Equator is a great circle.

Key facts

  • 01The Equator is 0° latitude.
  • 02The North Pole is 90° N.
  • 03The South Pole is 90° S.
  • 04Latitude can never be greater than 90°.
  • 05Lines joining positions of equal latitude are called parallels.
  • 06All parallels are parallel to the Equator.
  • 07The Equator is the only parallel that is a great circle.
03Section 3

Longitude — East or West

Longitude is the angular distance of a position east or west of the Prime Meridian. It is measured at the centre of the Earth between the Prime Meridian and the meridian passing through the position.

Interactive educational diagram

Longitude as an angle at the Earth's centre — polar view

Move the longitude slider to rotate the selected meridian. The angle λ is measured at the centre, from the Prime Meridian.

Earth seen from above the North PoleEducational diagram: the Earth viewed from above the North Pole, which is at the centre. The Prime Meridian runs from the centre to the top. The selected meridian at 045° E is drawn in purple, and the angle lambda between the two meridians is marked at the centre. The right half of the diagram is the Eastern Hemisphere and the left half the Western Hemisphere.λlongitude increases eastNorth PolePrime Meridian 000°180° meridian (approx. Date Line)EasternWestern
045° E
-180180

Coordinate

045° E

45° east of the Prime Meridian

Hemisphere

Eastern Hemisphere (suffix E)

The selected meridian and its anti-meridian (135° W) together form one great circle. Angle at the centre: 45° (0.785 rad).

Key facts

  • 01The Prime Meridian is 0° longitude.
  • 02Longitude is measured from 0° to 180° east or west.
  • 03All meridians meet at the North and South Poles.
  • 04Every complete meridian and its opposite meridian form a great circle.
  • 05The 180° meridian lies approximately along the International Date Line.
  • 06Meridians are not parallel.
04Section 4

Build a Coordinate

Move both sliders and watch the position, the hemispheres and the written coordinate update together.

Interactive educational diagram

Coordinate trainer — set a latitude and a longitude

Set both sliders, then read the coordinate. Elements on the far side of the Earth are drawn as dashed lines.

Interactive globe showing the selected positionEducational diagram: a circular Earth with the Equator drawn in red, the Prime Meridian in green, the selected parallel of latitude in blue and the selected meridian of longitude in purple. The amber marker P is the position 30° N, 045° E.P90° N90° S
30° N
-9090
045° E
-180180

Coordinate

30° N, 045° E

Latitude
30° north of the Equator
Longitude
45° east of the Prime Meridian

N / S hemisphere

Northern

E / W hemisphere

Eastern

This position lies 30° north of the Equator and 45° east of the Prime Meridian.

05Section 5

Degrees, Minutes and Seconds

Degrees alone are too coarse for navigation, so each degree is divided into minutes and each minute into seconds.

Anatomy of a coordinate

40°

Degrees

38′

Minutes

20″

Seconds

N

Hemisphere

Latitude example
40° 38′ 20″ N
Longitude example
022° 56′ 45″ E

A leading zero may be used for longitude so that it always occupies three digits: write 022° E rather than 22° E. This removes any possibility of confusing a latitude with a longitude.

Subdivisions

  • 1° = 60′
  • 1′ = 60″
  • 1° = 3600″

Common conversions

  • 30′ = 0.5°
  • 15′ = 0.25°
  • 45′ = 0.75°
  • 30″ = 0.5′

Interactive converter

Enter a value in degrees, minutes and seconds to see all three standard formats.

Coordinate type
Hemisphere
Degrees, minutes, seconds
40° 30′ 00.00″ N
Degrees and decimal minutes
40° 30.000′ N
Decimal degrees
40.5000° N
06Section 6

Coordinate Order

Latitude is always quoted first. A useful memory aid: you walk up the stairs (latitude) before you walk along the landing (longitude).

Put the coordinate in the correct order

Select the coordinate that is written first, then the second one.

Position 1
Position 2

Correct

40° 38′ N, 022° 56′ E

Incorrect order

022° 56′ E, 40° 38′ N

  • Latitude identifies the parallel.
  • Longitude identifies the meridian.
  • Their intersection identifies the position.
07Section 7

Worked Examples

Read each coordinate, decide on the hemispheres yourself, then reveal the answer.

Example 1

35° N, 020° E

In which hemispheres does this position lie, and how does it relate to the two reference lines?

  1. S1The latitude is 35° N. The suffix N means the position is north of the Equator.
  2. S2The longitude is 020° E. The suffix E means the position is east of the Prime Meridian.
  3. S3Both values are within limits: latitude ≤ 90°, longitude ≤ 180°.

Example 2

25° S, 130° E

Identify the hemispheres for this position.

  1. S1Latitude 25° S — the S suffix places it south of the Equator.
  2. S2Longitude 130° E — measured eastwards from Greenwich, still less than 180°.
  3. S3This is roughly central Australia, well inside the Eastern Hemisphere.

Example 3

51° N, 001° W

Identify the hemispheres and note the use of the leading zeros.

  1. S1Latitude 51° N — north of the Equator.
  2. S2Longitude 001° W — only 1° west of the Prime Meridian, written with leading zeros to three digits.
  3. S3A small longitude value still determines the hemisphere: W means Western.

Example 4

00° 00′, 000° 00′

What is special about this position?

  1. S1Latitude 00° 00′ places the position exactly on the Equator — neither north nor south.
  2. S2Longitude 000° 00′ places it exactly on the Prime Meridian — neither east nor west.
  3. S3There is therefore no hemisphere suffix at all for either coordinate.
08Section 8

Knowledge Check

Twelve questions in ATPL style. One retry is allowed per question, and you can restart the whole check at any time.

Question 1 of 12 · Multiple choice

Latitude

0/12

What is the maximum possible latitude?
09Section 9

Chapter Summary

Everything from this chapter on one screen.

Latitude

North or south of the Equator

Longitude

East or west of the Prime Meridian

Latitude range

0° to 90° N or S

Longitude range

0° to 180° E or W

Written order

Latitude first, longitude second

1 degree

60 minutes (1° = 60′)

1 minute

60 seconds (1′ = 60″)

Parallels

Never meet — all parallel to the Equator

Meridians

Meet at both poles — not parallel

Equator

0° latitude — the only parallel that is a great circle

Prime Meridian

0° longitude — through Greenwich

Chapter in progress

Work through the remaining sections and score at least 75% on the knowledge check to complete the chapter.

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