22
NAVIGATION — CHAPTER 22 · NOTES
Basics of Navigation
by Capt. Pankaj Pahil
✈ DGCA CPL / ATPL Exam Notes
Chapter 1
Direction, Latitude & Longitude
General Navigation · Ghost Aviator Series
By Capt. Pankaj Pahil | 17 Years of Teaching Excellence
Ghost Aviator
EASA / DGCA Syllabus
10 Topics Covered
Diagrams + Exam Tips
📋 Contents — Chapter 1
Shape of the Earth
Geodosy & Geoid Models
The Poles
Basic Direction
Sexagesimal System
Position Reference Systems
Circles on the Earth
Equator, Meridians & Graticule
Latitude
Geocentric & Geodetic Latitude
Special Parallels
Longitude
Difference in Longitude
Positions in Lat/Long
Lat/Long to Distance
Resolution Accuracy
Great Circle Vertices
Practice Questions
1
The Shape of the Earth
The Earth is not a perfect sphere. Its official shape is described as an oblate spheroid — a sphere slightly flattened at the poles due to centrifugal forces acting during its formation from a rotating gas cloud.
Oblate Spheroid: A sphere flattened at the poles and bulging at the equator. The flattening is called compression.
🔑 Key Values to Memorise:
Compression ≈ 0.3% (1/300th)
Polar diameter is 23 NM or 43 km less than equatorial diameter
Earth is also slightly pear-shaped — max diameter south of Equator
(Southern hemisphere distortion is in metres, not km)
Compression ≈ 0.3% (1/300th)
Polar diameter is 23 NM or 43 km less than equatorial diameter
Earth is also slightly pear-shaped — max diameter south of Equator
(Southern hemisphere distortion is in metres, not km)
Shapes and Their Cross-Sections
| Shape | Cross-Section | Math Complexity |
|---|---|---|
| Perfect Sphere | Circle | Simple |
| Oblate Spheroid | Ellipse | Moderate |
| Real Earth (Geoid) | Irregular | Complex |
✈ DGCA Exam Rule
For EASA / DGCA exam calculations, treat the Earth as a perfect sphere with:
Circumference = 21,600 NM or 40,000 km
Circumference = 21,600 NM or 40,000 km
Fig 1.1 — Four views of Earth's shape. For exams, use the sphere model.
2
Geodosy & Geoid Models
Geodosy is the science of measuring and modelling the Earth's shape. Different countries and agencies have created their own geoid models, each optimised for accuracy over a specific region.
Major Geoid Models
| Model | Used By |
|---|---|
| WGS 84 | USA / GPS / ICAO (World Standard) |
| OS36 | UK Ordnance Survey (survey of 1936) |
| NTF 1970 | France (Nouvelle Triangulation de France) |
| ED50 | European Datum 1950 (other EU countries) |
⚠ Important: Using different geoid models for the same position can produce errors of up to 200 metres (between ED50 and OS36 extremities). This matters for GPS and FMS accuracy!
Why WGS 84 Became the World Standard
GPS (24 satellites) — accuracy to tens of metres globally. Differences between geoids become significant at this precision.
FMS (Flight Management System) — uses IRS + DME ranging. If DME positions are stored in different datums (UK = OS36, France = NTF70), large position errors occur crossing the English Channel!
✅ ICAO adopted WGS 84 as the world standard. Modern navigation computers auto-correct for Earth shape distortions.
3
The Poles
The Poles are the extremities of the axis about which the Earth spins (the polar axis).
🔑 Key Fact: The polar axis is tilted at 23½° to the axis of Earth's orbit around the Sun. This tilt causes the seasons! (Covered fully in the "Time" chapter.)
Rotation as Seen from the Poles
| View from above | Rotation appears |
|---|---|
| North Pole | ANTI-CLOCKWISE (Counter-clockwise) |
| South Pole | CLOCKWISE |
✈ Exam Favourite
"When viewed from above the North Pole, the Earth rotates anticlockwise." This appears frequently in navigation exam questions.
Fig 1.2 — Earth's rotation seen from above each pole
4
Basic Direction on the Earth
Direction is defined starting from a datum — the direction of the Earth's spin, defined as East (hence, "sunrise in the East"). From this, all four cardinal directions follow:
Cardinal Points
N
North
Towards North Pole
Towards North Pole
E
East
Direction of spin
Direction of spin
S
South
Opposite North
Opposite North
W
West
Opposite East
Opposite East
Quadrantal Directions (midway between cardinal)
NE
SE
SW
NW
💡 Note: Cardinal & Quadrantal directions were used in maritime navigation but are too imprecise for air navigation. Aviation uses the Sexagesimal system instead.
Fig 1.3 — Cardinal (N,E,S,W) and Quadrantal (NE,SE,SW,NW) points
5
Sexagesimal System / True Direction
The Sexagesimal system measures direction as degrees of a clockwise rotation from North, giving a full 360° circle. This provides the precision required in air navigation.
000°
North
090°
East
180°
South
270°
West
🔑 True Direction: When measured from the geographic North Pole, direction is called True direction, suffixed with (T).
N = 000°(T) | E = 090°(T) | S = 180°(T) | W = 270°(T)
N = 000°(T) | E = 090°(T) | S = 180°(T) | W = 270°(T)
⚠ Always use 3-figure groups!
Write
Write
Write
090°(T) NOT 90°(T).Write
027° NOT 27° — a 2-digit bearing is ambiguous and should be treated as suspect.
Reciprocal Directions
The reciprocal of any bearing is the direction exactly 180° opposite.
Rule: Add or subtract 180° from the given bearing.
If result > 360°, subtract 360°. If result < 0°, add 360°.
Rule: Add or subtract 180° from the given bearing.
If result > 360°, subtract 360°. If result < 0°, add 360°.
Worked Examples
| Given Direction | Reciprocal | Working |
|---|---|---|
| 060°(T) | 240°(T) | 060 + 180 = 240 |
| 353°(T) | 173°(T) | 353 − 180 = 173 |
| 020°(T) | 200°(T) | 020 + 180 = 200 |
| 270°(T) | 090°(T) | 270 − 180 = 090 |
💡 Runway Designators: Runways are named at 10° intervals using the magnetic bearing divided by 10 (rounded). A runway at 273° magnetic = RW 27. Its reciprocal end = RW 09. Note: Runway directions use Magnetic North, not True North.
Fig 1.4 — Sexagesimal compass. Directions measured clockwise from North.
Bearing: 060° → Reciprocal: 240°
6
Position Reference Systems & Circles on the Earth
Position Reference System: A system that defines any position accurately and unambiguously on Earth's surface. For a sphere, linear (x,y) Cartesian co-ordinates are replaced by angular co-ordinates: Latitude and Longitude.
Great Circle vs Small Circle
| Feature | Great Circle | Small Circle |
|---|---|---|
| Centre & Radius | Same as Earth's | Different from Earth's |
| Size | Largest possible circle | Smaller than Great Circle |
| Navigation use | Shortest path between 2 points | Parallels of latitude |
| Example | Equator, Meridians | All parallels except Equator |
🔑 Critical Definition:
A Great Circle is a circle on Earth's surface whose centre and radius are those of the Earth itself.
The shortest distance between two points on Earth is the shorter arc of the Great Circle joining them.
Given two points, there is only ONE Great Circle joining them (unless they are diametrically opposite).
A Great Circle is a circle on Earth's surface whose centre and radius are those of the Earth itself.
The shortest distance between two points on Earth is the shorter arc of the Great Circle joining them.
Given two points, there is only ONE Great Circle joining them (unless they are diametrically opposite).
Fig 1.5 — Great Circle arc = shortest path between A and B
8
Equator, Meridians, Parallels & the Graticule
The Equator
The Great Circle whose plane is at 90° to the polar axis. It lies East-West and divides Earth into two equal hemispheres. The Equator is the datum (origin) for measuring Latitude.
Latitude origin = 0°
Meridians
Semi-Great Circles joining the North and South poles. Every Great Circle through the poles forms a meridian and its anti-meridian. All meridians indicate True North-South direction and cross the Equator at 90°.
The Prime (Greenwich) Meridian
The meridian passing through Greenwich, London. This is the datum (origin) for measuring Longitude.
Longitude origin = 0°
Parallels of Latitude
Small circles whose planes are parallel to the Equator. They lie East-West and indicate position North or South of the Equator.
Exception: The Equator itself is the only parallel of latitude that is also a Great Circle.
The Graticule
The network formed by the Prime Meridian + all meridians + Equator + all parallels of latitude. It is the spherical equivalent of the x-y grid on graph paper. Position is defined in degrees/minutes/seconds, not by distance.
Fig 1.6 — The Graticule: Meridians (vertical) + Parallels (horizontal) + Equator
9
Latitude
Latitude of any point is the arc (angular distance) measured along the meridian through that point, from the Equator to the point.
Expressed in degrees, minutes, and seconds of arc.
Annotated N (north of Equator) or S (south of Equator).
Expressed in degrees, minutes, and seconds of arc.
Annotated N (north of Equator) or S (south of Equator).
Range of Latitude Values
| Location | Latitude Value |
|---|---|
| Equator | 0° (neither N nor S) |
| North Pole | 90°N |
| South Pole | 90°S |
Angular Measurement System
| Unit | Subdivision | Symbol |
|---|---|---|
| Degree | 1/360th of circle | ° |
| Minute of arc | 1/60th of degree | ʹ |
| Second of arc | 1/60th of minute | ˮ |
✈ Key Exam Distinction
Position is measured in degrees, minutes, and seconds.
Direction is measured in degrees and decimal degrees.
Direction is measured in degrees and decimal degrees.
How to Find a Parallel of Latitude
From Earth's centre, construct a line with an elevation angle (for N latitudes) or depression angle (for S latitudes) equal to the desired latitude.
Where this line touches the Earth's surface = that parallel of latitude.
Where this line touches the Earth's surface = that parallel of latitude.
Interactive: Latitude Finder
Latitude: 28°N (approx. New Delhi, India)
Fig 1.7 — Latitude is the angle at Earth's centre between the Equator and the point
10
Geocentric & Geodetic Latitude
Two Types of Latitude
| Type | Definition | Used on Charts? |
|---|---|---|
| Geocentric | Angle between the line from point to Earth's centre and the Equatorial plane | No |
| Geodetic (Geographic) | Angle between the normal (perpendicular) to the spheroid surface at the point and the Equatorial plane | YES ✓ |
🔑 Important Difference:
For a perfect sphere, these two would be identical. Because Earth is an oblate spheroid, the "normal" at a surface point does not pass through Earth's centre.
For a perfect sphere, these two would be identical. Because Earth is an oblate spheroid, the "normal" at a surface point does not pass through Earth's centre.
⚠ Maximum Difference:
Geocentric vs Geodetic latitude differs most at approximately 45°N/S and the maximum difference is about 11.6 minutes of arc (~11.6 NM on the surface — significant for precision navigation!).
Geocentric vs Geodetic latitude differs most at approximately 45°N/S and the maximum difference is about 11.6 minutes of arc (~11.6 NM on the surface — significant for precision navigation!).
💡 Navigation charts use Geodetic latitude. Modern navigation computers (GPS, FMS, IRS) automatically account for this.
Fig 1.8 — Geocentric (red) vs Geodetic (green) latitude
11
Special Cases of Parallels of Latitude
Four special parallels are defined based on Earth's 23½° axial tilt. They relate to the seasons and periods of daylight throughout the year.
Arctic Circle
66½°N
= 90° − 23½°. At summer solstice, sun never sets above this line.
Antarctic Circle
66½°S
= 90° − 23½°. At winter solstice (NH), sun never rises above this line.
Tropic of Cancer
23½°N
Sun is directly overhead on June 21 (NH mid-summer / summer solstice).
Tropic of Capricorn
23½°S
Sun is directly overhead on Dec 21 (NH mid-winter / winter solstice).
Fig 1.9 — The four special parallels of latitude (not to scale)
✈ Memory Aid
66½° = 90° − 23½° (Earth's tilt). Notice that Arctic/Antarctic and Tropic values are complementary (add up to 90°). Also: Cancer is North (C-N), Capricorn is South (C-S).
12
Longitude
Longitude of any point is the shorter arc along the Equator between the Prime Meridian and the meridian through the point.
Measured in degrees and minutes of arc.
Annotated E (east of Greenwich) or W (west of Greenwich).
Measured in degrees and minutes of arc.
Annotated E (east of Greenwich) or W (west of Greenwich).
Range of Longitude Values
| Location | Longitude Value |
|---|---|
| Prime Meridian (Greenwich) | 000° |
| Maximum East | 180°E |
| Maximum West | 180°W |
| Anti-Meridian (coincident) | 180°E = 180°W |
🔑 Key Comparison — Latitude vs Longitude:
Latitude lines are all parallel to each other. Think: "slicing a pineapple"
Longitude lines fan from N Pole, max separation at Equator, converge at S Pole. Think: "segmenting an orange"
Latitude lines are all parallel to each other. Think: "slicing a pineapple"
Longitude lines fan from N Pole, max separation at Equator, converge at S Pole. Think: "segmenting an orange"
Reversal at 180°E (Anti-Meridian)
⚠ Confusing but Exam-Tested!
At the Greenwich Meridian: Eastern longitudes are to your East.
At the 180° meridian: Eastern longitudes are now to your WEST and Western longitudes to your EAST!
The direction East (090°T) has NOT changed — it is still the direction of Earth's spin. Only the apparent position of E/W hemispheres reverses.
At the Greenwich Meridian: Eastern longitudes are to your East.
At the 180° meridian: Eastern longitudes are now to your WEST and Western longitudes to your EAST!
The direction East (090°T) has NOT changed — it is still the direction of Earth's spin. Only the apparent position of E/W hemispheres reverses.
Fig 1.10 — Longitude viewed from above North Pole. Point B is at 040°E.
13
Difference in Longitude (Ch Long)
Rules for Calculating Change of Longitude (Ch Long)
RULE 1 — Same side (both E or both W):
Example: 100°W and 080°W → 100 − 80 = 20°
Ch Long = Larger − SmallerExample: 100°W and 080°W → 100 − 80 = 20°
RULE 2 — Different sides (one E, one W):
Example: 020°W and 010°E → 20 + 10 = 30°
Ch Long = E value + W valueExample: 020°W and 010°E → 20 + 10 = 30°
⚠ Special Case near 180° Anti-Meridian:
When positions straddle 180°, the calculated total may exceed 180°.
ALWAYS take the SHORTER arc.
Example: 163°E and 152°W
163 + 152 = 315° (this is the long way round!)
Ch Long = 360° − 315° = 45°
When positions straddle 180°, the calculated total may exceed 180°.
ALWAYS take the SHORTER arc.
Example: 163°E and 152°W
163 + 152 = 315° (this is the long way round!)
Ch Long = 360° − 315° = 45°
Worked Examples
| Position 1 | Position 2 | Ch Long | Method |
|---|---|---|---|
| 040°E | 070°E | 030° | Same side: 70−40 |
| 030°W | 100°W | 070° | Same side: 100−30 |
| 020°E | 050°W | 070° | Diff sides: 20+50 |
| 163°E | 152°W | 045° | 360−(163+152)=45 |
| 170°E | 160°W | 030° | 360−(170+160)=30 |
Fig 1.11 — Calculating Ch Long. Red arc = same side (30°). Purple arc = short way round 180° (45°).
to
14
Positions in Latitude & Longitude
🔑 Rule: Latitude ALWAYS comes first, then Longitude!
New York:
Delhi (IGI) ARP:
New York:
41°N 074°WDelhi (IGI) ARP:
28°34'N 077°07'E
Formats for Expressing Position
| Format | Example | Precision |
|---|---|---|
| Degrees only | 41N 074W | ~1° |
| Deg + Minutes | 4100N 07400W | ~1 NM |
| Decimal minutes | 5150.2N 00119.3W | 0.1 NM |
| Deg/Min/Sec (DMS) | 515013N 0011912W | ~100 ft |
| DMS decimal | 515000.28N 001924.45W | <1 metre |
Indian Pilot Locations (Examples)
| Location | Approx Position |
|---|---|
| Delhi (Indira Gandhi Intl) | 2832N 07708E |
| Mumbai (CSIA) | 1906N 07251E |
| Bangalore (Kempegowda) | 1314N 07732E |
| Chennai (MAA) | 1300N 08010E |
| Kolkata (CCU) | 2238N 08826E |
Fig 1.12 — Major Indian airport positions (approximate)
15
Conversion of Latitude & Longitude to Distance
Nautical Mile (NM): Defined so that 1 minute of arc on a Great Circle = 1 NM.
1 NM = 6080 feet = 1852 metres (ICAO standard)
This arises because Earth's mean radius ≈ 20.9 million feet.
1 NM = 6080 feet = 1852 metres (ICAO standard)
This arises because Earth's mean radius ≈ 20.9 million feet.
🔑 Converting Latitude Difference to Distance:
Since all meridians are Great Circles:
Example: 50°00'N to 50°05'N = 5 NM
Since all meridians are Great Circles:
1 minute of latitude change = 1 NM1 degree of latitude change = 60 NMExample: 50°00'N to 50°05'N = 5 NM
⚠ Longitude is DIFFERENT!
This 1 minute = 1 NM rule applies to longitude ONLY at the Equator (because the Equator is the only parallel that is also a Great Circle). At all other latitudes, parallels are Small Circles and the formula is different.
This 1 minute = 1 NM rule applies to longitude ONLY at the Equator (because the Equator is the only parallel that is also a Great Circle). At all other latitudes, parallels are Small Circles and the formula is different.
Quick Reference
| Angular Change | Distance on Meridian |
|---|---|
| 1 second (1") | ≈ 101 feet ≈ 30 metres |
| 0.1 minute (0.1') | ≈ 608 feet ≈ 185 metres |
| 1 minute (1') | 1 NM = 6080 feet = 1852 m |
| 1 degree (1°) | 60 NM = 111.1 km |
| 90° | 5400 NM (Equator to Pole) |
| 360° | 21,600 NM (circumference) |
Fig 1.13 — On any meridian, 1 minute of arc = 1 nautical mile
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Resolution Accuracy Using Latitude & Longitude
The number of decimal places used when writing a position declares the accuracy (resolution) being claimed. Each format corresponds to a real-world precision:
🔑 Two ways to express sub-minute positions:
1. Decimal minutes: 5150.2N (1 decimal place = 0.1 NM = 608 ft = 185 m)
2. DMS: 51°50'12"N (1 second = ~101 ft = ~30 m)
1. Decimal minutes: 5150.2N (1 decimal place = 0.1 NM = 608 ft = 185 m)
2. DMS: 51°50'12"N (1 second = ~101 ft = ~30 m)
💡 Practical Note: Modern cockpit systems (INS, IRS, FMS, GPS) use decimal minutes. Large-scale charts use DMS. The system can express position from 1 NM (en route) to 50 cm (ILS calibration) — same format, just more digits!
✈ DGCA MCQ Tip
"A position given as
"A position entered into an FMS/GPS is to the nearest decimal minute, implying accuracy of 0.1 NM = 600 feet."
"The ARP of an aerodrome quoted in the AIP as
5321N implies an accuracy of approximately 1 NM.""A position entered into an FMS/GPS is to the nearest decimal minute, implying accuracy of 0.1 NM = 600 feet."
"The ARP of an aerodrome quoted in the AIP as
515013N 0011912W is accurate to the nearest second of arc = 100 feet = 30 metres."
17
Great Circle Vertices
Vertex: The most northerly (or southerly) point of a Great Circle. Every Great Circle has a Northern Vertex and a Southern Vertex, which are antipodal (diametrically opposite).
🔑 Key Properties of Vertices:
1. Vertices are antipodal — same latitude, opposite longitude (±180°)
2. Distance between vertices = 10,800 NM (half Earth's circumference)
3. At either vertex, the Great Circle direction is 090°(T) or 270°(T) — i.e., the GC runs East-West at the vertex
4. Vertices lie on a meridian and its anti-meridian
1. Vertices are antipodal — same latitude, opposite longitude (±180°)
2. Distance between vertices = 10,800 NM (half Earth's circumference)
3. At either vertex, the Great Circle direction is 090°(T) or 270°(T) — i.e., the GC runs East-West at the vertex
4. Vertices lie on a meridian and its anti-meridian
Finding the Other Vertex
If Southern Vertex = 63°S 170°W
Then Northern Vertex = 63°N and longitude = 170° − 180° = −10° = 010°E
Rule: Same latitude number, opposite N/S. Longitude ± 180°.
Then Northern Vertex = 63°N and longitude = 170° − 180° = −10° = 010°E
Rule: Same latitude number, opposite N/S. Longitude ± 180°.
Equator Crossing Points
A Great Circle crosses the Equator at two points, each at a longitude 90° Ch Long from either vertex.
Example: Northern vertex at 63°N 010°E
→ Crosses Equator at: 010°E ± 90° = 100°E and 080°W
Example: Northern vertex at 63°N 010°E
→ Crosses Equator at: 010°E ± 90° = 100°E and 080°W
Track Angle at Equator Crossing
At the Equator crossing, the angle = latitude of the vertex.
Travelling East from N vertex:
First crossing: Track = 090° + vertex_lat
Second crossing: Track = 090° − vertex_lat
Travelling West from N vertex: Use reciprocals (+180°)
Travelling East from N vertex:
First crossing: Track = 090° + vertex_lat
Second crossing: Track = 090° − vertex_lat
Travelling West from N vertex: Use reciprocals (+180°)
Worked Example (63°N vertex, tracking East)
| Crossing | Longitude | Track °(T) | Working |
|---|---|---|---|
| 1st (southbound) | 080°W | 153° | 090+63=153 |
| 2nd (northbound) | 100°E | 027° | 090−63=027 |
Two Special Cases
| Vertex Latitude | Type of GC | Equator crossing angle |
|---|---|---|
| 90°N/S | Meridian | 180° or 000° |
| 0°N/S | Equator itself | 0° (it IS the Equator), direction 090° or 270° |
Fig 1.14 — Great Circle vertices, crossing points, and track angles at Equator
Fig 1.15 — Track angles at first and second Equator crossings (tracking East)
18
Practice Questions & Answers (DGCA Style)
Solved Practice Questions
Q1
What is the approximate compression of the Earth?
a) 3% b) 0.03% c) 0.3% d) 1/3000
a) 3% b) 0.03% c) 0.3% d) 1/3000
Q2
A Graticule is the name given to:
a) A series of lines drawn on a chart
b) A series of Latitude and Longitude lines drawn on a chart or map
c) A selection of small circles as you get nearer to either pole
a) A series of lines drawn on a chart
b) A series of Latitude and Longitude lines drawn on a chart or map
c) A selection of small circles as you get nearer to either pole
Q3
A great circle has its North vertex at 70°N 130°E. What is the position of its South vertex?
Answer: 70°S 050°W
Same latitude number (70), opposite S. Longitude: 130E − 180 = −50 = 050°W
Answer: 70°S 050°W
Same latitude number (70), opposite S. Longitude: 130E − 180 = −50 = 050°W
Q4a
GC with N vertex at 70°N 130°E. Equator crossing longitudes (initial direction EAST from N vertex)?
Crossing longitudes: 130°E ± 90° = 040°E and 140°W
Track at 1st crossing (Eastbound): 090 + 70 = 160°(T)
Crossing longitudes: 130°E ± 90° = 040°E and 140°W
Track at 1st crossing (Eastbound): 090 + 70 = 160°(T)
Q4b
Same GC, initial direction WEST from N vertex?
Crossings still at 040°E and 140°W
Tracks = reciprocals: 200°(T) and 340°(T)
Crossings still at 040°E and 140°W
Tracks = reciprocals: 200°(T) and 340°(T)
Q5
Compression = 1/297, semi-major axis = 6378.4 km. Find polar semi-minor axis.
Formula: polar = equatorial × (1 − 1/compression)
= 6378.4 × (1 − 1/297)
= 6378.4 × 0.99663
= 6356.9 km → Answer: b
Formula: polar = equatorial × (1 − 1/compression)
= 6378.4 × (1 − 1/297)
= 6378.4 × 0.99663
= 6356.9 km → Answer: b
Additional Practice (DGCA MCQ Style)
Q6: The shortest distance between two points on Earth is along:
→ The shorter arc of the Great Circle joining them
→ The shorter arc of the Great Circle joining them
Q7: The Equator is special because it is the only parallel of latitude that is also a:
→ Great Circle
→ Great Circle
Q8: At a Great Circle vertex, the direction of the Great Circle is:
→ 090°(T) or 270°(T) — East or West
→ 090°(T) or 270°(T) — East or West
Q9: The difference in longitude between 040°E and 055°W is:
Different sides → 40 + 55 = → 095°
Different sides → 40 + 55 = → 095°
Q10: ICAO has adopted which datum as the world standard for GPS?
→ WGS 84
→ WGS 84
Q11: 1 minute of arc along a meridian equals approximately:
→ 1 Nautical Mile (1 NM = 1852 m)
→ 1 Nautical Mile (1 NM = 1852 m)
Q12: The maximum difference between Geocentric and Geodetic latitudes is approximately 11.6 minutes and occurs at approximately:
→ 45°N/S
→ 45°N/S
💡 Quick Summary Table
| Concept | Key Number |
|---|---|
| Earth compression | 0.3% or 1/300 |
| Polar diameter less than equatorial | 23 NM / 43 km |
| Earth circumference (exam) | 21,600 NM / 40,000 km |
| 1 NM | 1852 m / 6080 ft |
| 1° of Great Circle arc | 60 NM |
| Max geocentric/geodetic diff | 11.6' at 45°N/S |
| Tropic latitudes | 23½°N and S |
| Polar circle latitudes | 66½°N and S |
| Earth's axial tilt | 23½° |
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