What Is Magnetic Declination?

by Christopher O'Keeffe June 04, 2026

Why your compass does not point to the same north shown on your map — and why every bushwalker, navigator, sailor, surveyor and outdoor traveller should understand the difference.

A compass is one of the most reliable navigation tools ever invented.

It does not need batteries.

It does not need mobile reception.

It does not need satellites.

But there is one important thing every navigator must understand:

A compass does not point to true north.

It points to magnetic north.

That difference is called magnetic declination.

For casual use, the difference may not seem important. But when navigating with a topographic map, marine chart, compass, GPS, or bearing over distance, magnetic declination can make a real difference.

A few degrees of error may not matter when walking across a car park. But in the bush, on the water, in remote country, or across a long bearing, a small error can gradually become a very large mistake.

At Mapworld, we supply topographic maps, nautical charts, compasses, navigation tools, and field-ready mapping products for people who rely on accurate direction. Understanding magnetic declination is one of the foundations of proper map-and-compass navigation.

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What Is Magnetic Declination?

Magnetic declination is the angle between true north and magnetic north.

True north is the direction of the geographic North Pole.

Magnetic north is the direction your compass needle points.

These are not the same.

NOAA’s National Centers for Environmental Information defines magnetic declination, also called magnetic variation, as the angle between magnetic north and true north. Declination is east when magnetic north lies east of true north, and west when it lies west of true north. It also changes over time and varies by location.

That means the magnetic declination in Perth is different from the magnetic declination in Sydney, Brisbane, Hobart, Darwin or central Australia.

It also means the declination printed on an older map may no longer be perfectly current.

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The Three Norths: True North, Grid North and Magnetic North

One of the first things to understand is that navigators often deal with three different norths.

True North

True north points to the geographic North Pole.

This is the north used by lines of longitude on the globe.

Grid North

Grid north refers to the north direction of the map’s grid lines.

On many topographic maps, grid north is close to true north, but not always identical.

Magnetic North

Magnetic north is the direction indicated by a compass needle.

Because the Earth’s magnetic field is not aligned perfectly with the geographic poles, magnetic north differs from true north.

Geoscience Australia’s topographic map layout guidance includes a magnetic declination diagram showing True North, Grid North and Magnetic North values for the centre of a map sheet.

This small diagram is one of the most important pieces of information on a topographic map.

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Why Magnetic Declination Matters

When you use a compass with a map, you are often moving between two systems:

• The map, which is usually based on grid north or true north

• The compass, which points to magnetic north

If you do not correct for declination, your bearing may be wrong.

The larger the declination and the longer the distance, the greater the error becomes.

For example, if your bearing is out by only 5 degrees, you may still end up hundreds of metres off course over a long walk. In thick bush, poor visibility, steep terrain or remote country, that matters.

Magnetic declination is particularly important for:

• Bushwalking

• Off-track navigation

• Search and rescue

• Four-wheel-driving

• Surveying

• Fieldwork

• Marine navigation

• Outdoor education

• Military and cadet training

• Remote-area travel

Good navigation is not just about having a compass.

It is about knowing how to use it correctly.

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East Declination and West Declination

Magnetic declination is usually described as either east or west.

East Declination

Magnetic north lies east of true north.

West Declination

Magnetic north lies west of true north.

The correction you apply depends on whether declination is east or west and whether you are converting from map to compass or compass to map.

This is where many beginners become confused.

A common navigation phrase is:

Grid to magnetic: add or subtract depending on local declination.

However, because different training systems use different memory aids, and because mistakes can be serious, it is always best to follow the declination diagram and instructions printed on your map or taught by a qualified navigation instructor.

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Magnetic Declination Changes by Location

Magnetic declination is not the same everywhere.

It varies across Australia and across the world because the Earth’s magnetic field varies geographically.

NOAA notes that declination changes with location as well as over time.

This is why you should not assume that the declination you used on one trip will be correct somewhere else.

A walker in New South Wales, a sailor in Western Australia, a surveyor in Queensland and a traveller in Tasmania may all be working with different magnetic declination values.

For Australian navigation, Geoscience Australia provides tools and models relating to the Australian magnetic field, including calculators for magnetic declination. NSW Spatial Services also links to Geoscience Australia’s AGRF calculator for determining current magnetic declination at any location using the Australian Geomagnetic Reference Field.

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Magnetic Declination Changes Over Time

Magnetic declination is not fixed.

It slowly changes because the Earth’s magnetic field changes.

Geoscience Australia explains that it monitors Earth’s changing magnetic field in the Australian region and updates the Australian Geomagnetic Reference Field model at five-year intervals.

This matters because the declination printed on an older paper map may no longer be exact.

Most topographic maps include:

• The magnetic declination at a particular date

• The annual rate of change

• A diagram showing true, grid and magnetic north

If the map is older, you may need to update the declination value before navigating precisely.

This is one reason current maps and modern compasses remain important for serious navigation.

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Where to Find Magnetic Declination on a Topographic Map

On most topographic maps, magnetic declination information appears in the map margin.

Look for a diagram showing:

• True North

• Grid North

• Magnetic North

• The angle between them

• The date of the magnetic information

• The annual change, where provided

On Geoscience Australia-style topographic map products, the marginal information includes this magnetic declination diagram for the centre of the sheet.

Before using your compass with a map, take a moment to read that diagram.

It tells you how the compass world and map world relate to one another.

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Magnetic Declination and Topographic Maps

Magnetic declination is especially important when using topographic maps.

Topographic maps often show:

• Contours

• creeks

• ridges

• tracks

• roads

• grid lines

• spot heights

• vegetation

• boundaries

• landforms

When navigating in the field, you may take a bearing from the map and then follow it with a compass.

If the map bearing is based on grid north and your compass points to magnetic north, you must correct between the two.

This is one of the reasons quality compasses often include:

• Rotating bezels

• Declination scales

• Baseplates

• Direction-of-travel arrows

• Map scales

• Sighting mirrors on advanced models

A compass is much more powerful when paired with a proper topographic map and a sound understanding of declination.

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Magnetic Declination and Nautical Charts

Magnetic declination also matters at sea.

On nautical charts, the term magnetic variation is often used.

This refers to the same basic concept: the angle between true north and magnetic north.

Marine navigators must understand magnetic variation when working with:

• Compass courses

• Bearings

• Charted directions

• Navigation lights

• Leading lines

• Course plotting

• Deviation and variation corrections

In marine navigation, there is also another issue called deviation, which is compass error caused by magnetic influences aboard the vessel itself.

A skipper may need to account for both variation and deviation when converting between chart bearings and compass courses.

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Magnetic Declination vs Compass Deviation

These two terms are often confused.

Magnetic Declination

Caused by the difference between true north and magnetic north.

It varies by location and time.

Compass Deviation

Caused by local magnetic interference near the compass.

On a boat, vehicle or aircraft, deviation may be caused by:

• Metal

• electronics

• engines

• wiring

• speakers

• tools

• magnetic objects

Declination comes from the Earth’s magnetic field.

Deviation comes from the equipment or environment around the compass.

Both can affect navigation.

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A Simple Example

Imagine you are using a topographic map and compass on a bushwalk.

You draw a route on the map and determine a grid bearing.

But your compass needle points to magnetic north, not grid north.

If the local magnetic declination is significant and you do not correct for it, your real walking direction will be slightly wrong.

At first, nothing may seem unusual.

After 50 metres, you may still feel on track.

After 500 metres, the error grows.

After several kilometres, you may be far from where you intended to be.

This is why magnetic declination matters most over distance.

The longer the bearing, the more important accuracy becomes.

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Do You Always Need to Adjust for Declination?

Not always.

If you are walking on a clear, well-marked track and simply using a compass to confirm general direction, declination may not be critical.

But you should understand it.

You should adjust for declination when:

• Navigating off-track

• Following a bearing over distance

• Travelling in poor visibility

• Crossing featureless terrain

• Navigating at night

• Working in remote country

• Plotting routes precisely

• Teaching navigation

• Conducting fieldwork

• Navigating at sea

The more serious the navigation, the more important declination becomes.

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How to Deal with Magnetic Declination

There are three common approaches.

1. Use the Declination Diagram on Your Map

This is the traditional method.

Read the map’s magnetic diagram and apply the correct adjustment when converting between map bearings and compass bearings.

2. Use a Compass with Declination Adjustment

Some compasses allow you to set the local declination.

Once set correctly, the compass helps compensate for the difference between magnetic north and map north.

This is especially useful for regular navigators.

3. Check a Current Declination Calculator

Because declination changes over time, current calculators can help confirm the latest value for a location.

Geoscience Australia provides magnetic field calculation tools for the Australian region, and NOAA provides magnetic declination products and calculators internationally.

For serious navigation, always use reliable official sources and current maps.

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Why Older Maps Need Care

Older maps can still be excellent references.

Historical maps, older topographic sheets and archived charts often contain valuable information.

But when using an older map for navigation, magnetic information may be outdated.

Because magnetic declination changes over time, the angle printed on an older map may no longer be accurate.

For display or historical interest, this does not matter.

For serious navigation, it does.

This is why bushwalkers, field professionals and mariners should use current mapping and verify current magnetic information when accuracy matters.

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Magnetic Declination in Australia

Australia is a large country, and magnetic declination varies widely from place to place.

This is especially relevant for people travelling between states or working across remote areas.

A compass user moving between Western Australia, Queensland, New South Wales, Tasmania and the Northern Territory cannot assume the same declination value applies everywhere.

Geoscience Australia maintains geomagnetic observatories and models to monitor changes in the Australian magnetic field, supporting navigation, surveying, geophysical exploration and other applications.

For Mapworld customers, the practical lesson is simple:

Check the declination for the map and region you are actually using.

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Magnetic Declination and GPS

GPS has changed navigation, but it has not made magnetic declination irrelevant.

GPS devices can display direction in different ways, including true bearings and magnetic bearings depending on settings.

A GPS may know where you are, but if you are translating between a GPS bearing, a paper map and a handheld compass, you still need to understand what kind of north each system is using.

This is especially important when combining:

• GPS

• topographic maps

• paper charts

• compasses

• route notes

• grid references

• field bearings

Good navigators do not rely blindly on a device.

They understand the reference system behind the information.

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Compass Buying Tip: Look for Declination Features

If you regularly navigate with maps, consider a compass that supports declination work.

Useful features include:

• Rotating bezel

• Clear baseplate

• Map scales

• Declination scale

• Adjustable declination on some models

• Sighting mirror for precision bearings

• Luminous markings for low light

At Mapworld, compass ranges such as Silva are popular because they are designed for real map-and-compass navigation, from beginner bushwalking to professional expedition use.

For casual walkers, a simple baseplate compass may be enough.

For serious navigation, a higher-quality compass with declination features is a worthwhile investment.

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Mapworld’s Recommendation

If you are learning navigation, do not treat magnetic declination as an advanced topic.

It is fundamental.

Start with:

1. A current topographic map

2. A quality compass

3. The declination diagram on the map

4. A basic understanding of true, grid and magnetic north

5. Practice in simple terrain before relying on it in remote country

Navigation is a skill.

It improves with repetition.

The more you work with maps and compasses, the more natural declination becomes.

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Final Thoughts

Magnetic declination is a small angle with big consequences.

It is the difference between where your map says north is and where your compass points.

For casual navigation, it may seem like a technical detail.

For serious navigation, it is essential.

Understanding magnetic declination helps you use topographic maps, nautical charts, compasses and GPS systems more intelligently.

It helps you avoid small errors becoming large ones.

It helps you navigate with confidence.

And it reminds us that good navigation is never just about owning the right equipment.

It is about understanding what that equipment is telling you.

Because a compass is simple.

But using it well is a skill.

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Frequently Asked Questions

What is magnetic declination?

Magnetic declination is the angle between true north and magnetic north. It is the difference between the direction shown by geographic north on a map and the direction your compass needle points.

Is magnetic declination the same everywhere?

No. Magnetic declination changes depending on where you are. It also changes slowly over time.

Why does magnetic declination matter?

It matters because maps are usually aligned to true north or grid north, while a compass points to magnetic north. If you do not correct for the difference, your bearing may be inaccurate.

Where do I find magnetic declination on a map?

Most topographic maps include a magnetic declination diagram in the margin showing True North, Grid North and Magnetic North for the map sheet.

Does magnetic declination change over time?

Yes. The Earth’s magnetic field changes over time. Geoscience Australia updates its Australian Geomagnetic Reference Field model at five-year intervals to monitor these changes in the Australian region.

Is magnetic declination important for bushwalking?

Yes, especially for off-track navigation, poor visibility, long bearings, remote terrain and serious map-and-compass use.

Is magnetic declination important for boating?

Yes. In marine navigation it is often called magnetic variation and is used when converting between charted bearings and compass courses.

Can GPS replace knowledge of magnetic declination?

No. GPS is useful, but if you are working between GPS bearings, paper maps and a compass, you still need to understand whether each system is using true north, grid north or magnetic north.

What compass should I use for declination work?

A quality baseplate compass is suitable for beginners. More advanced navigators may prefer compasses with declination scales, adjustable declination, sighting mirrors or expedition features.

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