How does Magnetic North differ from True North?

Magnetic North is the direction indicated by a magnetic compass, pointing towards the Earth's magnetic pole, which is offset from True North.

What is Grid North and when is it used?

Grid North is the direction northwards along the grid lines of a map projection, commonly used in polar regions where meridians converge.

How do variation and deviation affect compass readings?

Variation is the angular difference between True and Magnetic North, while deviation is the error between Magnetic and Compass North caused by local magnetic influences.

Why is understanding the different north references important in aviation?

Accurate navigation and heading calculations require pilots to correctly apply corrections for variation and deviation, ensuring safe and precise flight paths.

Compass Norths: True, Magnetic, Grid

Q: What is True North in aviation navigation?

True North refers to the direction along the Earth's surface towards the geographic North Pole, used as a constant reference on charts.

Medium4 min readGeneral Navigation

Moderately Examined

Why this matters

Accurate navigation depends on knowing which north reference to use and how to convert between them. Misunderstanding these differences can lead to significant heading errors, especially in regions with large magnetic variation or when using grid-based charts.

In aviation, understanding the three main north references—true north, magnetic north, and grid north—is essential for accurate navigation. Each 'north' provides a different directional baseline: true north aligns with the Earth's geographic pole, magnetic north points to the magnetic pole where compasses are attracted, and grid north is used on certain map projections for practical chartwork. Pilots must know how these norths differ and how to convert between them to ensure precise headings and safe flight planning.

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In depth

Explanation

True North

True north (TN) is the direction along the Earth's surface towards the geographic North Pole, where all meridians of longitude converge. It is the fixed reference for geographic coordinates and is used as the baseline for most aeronautical charts and navigation calculations.

Magnetic North

Magnetic north (MN) is the direction indicated by a magnetic compass, pointing toward the Earth's magnetic north pole. This pole does not coincide with the geographic North Pole and slowly shifts over time due to changes in the Earth's magnetic field. The angle between true north and magnetic north at any location is called variation (or magnetic declination). Variation can be east or west, and its value is marked on aeronautical charts, often with isogonals (lines of equal variation).

Grid North

Grid north is used on charts with a grid system, such as the Lambert Conformal or Transverse Mercator projections. It is the direction of the vertical grid lines on the chart, which may not align perfectly with true north except along a specific meridian called the central meridian. Grid north simplifies plotting and measuring directions on large-scale maps, especially in polar regions where meridians converge sharply.

Compass North and Corrections

A magnetic compass in an aircraft points toward magnetic north, but is also affected by local magnetic fields within the aircraft, causing compass deviation. The sequence for converting between compass heading, magnetic heading, and true heading is:

Compass Heading (CH) ± Deviation = Magnetic Heading (MH)
Magnetic Heading (MH) ± Variation = True Heading (TH)

Remember: Deviation is the angle between compass north and magnetic north; variation is the angle between magnetic north and true north.

Practical Use

Pilots must apply deviation and variation corrections when converting between compass, magnetic, and true headings. Grid north becomes important when operating in areas where chart projections distort the relationship between true and magnetic north, such as at high latitudes.

The essentials

Key Points

True north is the direction toward the geographic North Pole.

Magnetic north is where a compass needle points, toward the Earth's magnetic pole.

Grid north is the direction of the grid lines on certain map projections, used for chartwork.

Variation is the angle between true north and magnetic north; it changes with location and time.

Deviation is the error between compass north and magnetic north, caused by local magnetic influences.

Pilots must apply deviation and variation corrections to convert between compass, magnetic, and true headings.

Grid north is primarily used in high-latitude or grid-based chart regions.

Watch out

Exam Traps & Typical Mistakes

Confusing variation (true vs magnetic) with deviation (magnetic vs compass).

Assuming magnetic north and true north are the same everywhere.

Forgetting that grid north may not align with true north except along the central meridian.

Believing that the direction of variation (east or west) depends on hemisphere—it does not.

Assuming compass north can be directly related to true north without knowing both deviation and variation.

Test yourself

Example Exam Questions

Question 2Medium

Compass North differs from Magnetic North due to which factor?

Question 3Easy

Which north reference is aligned with the Earth's axis of rotation?

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