True Bearing – Direction Relative to True North (Navigation)

Definition of True Bearing

True Bearing is a cornerstone navigational concept: it is the horizontal angle measured clockwise from True North—the Earth’s geographic North Pole—to a target or object. Expressed in degrees from 000° (True North) to 359°, true bearing is foundational in aviation, marine, and land navigation.

For example:

• 000°T: True North
• 090°T: Due East
• 180°T: Due South
• 270°T: Due West

True bearings provide a universal standard, unaffected by local anomalies or changes in Earth’s magnetic field. Charts and maps are oriented to True North, making true bearings essential for plotting courses, synchronizing data, and communicating directions accurately across systems.

In aviation, all flight plans, charts, and most air traffic control instructions use true bearings. Maritime navigation relies on it for chart work, and land navigation uses it for reliable map-to-field orientation.

A true bearing is always annotated with a “T” (e.g., 075°T) to distinguish it from other bearing types.

Types of North: True, Magnetic, and Grid North

Clear understanding of the three main “North” references is essential for accurate navigation.

True North (Geographic North)

• Definition: Direction to Earth’s geographic North Pole (axis of rotation).
• Symbol: TN
• Use: Standard for charts, celestial navigation, GPS, and most map work.
• Stability: Fixed—does not change over time or place.

All meridians (longitude lines) on maps point to True North. The North Star (Polaris) closely aligns with True North, aiding celestial navigation.

Magnetic North

• Definition: Direction a compass needle points, following Earth’s magnetic field.
• Symbol: MN
• Use: Compass navigation, field work, and runway designations.
• Stability: Moves over time due to shifts in Earth’s core and field (over 50 km/year recently).

Magnetic bearings must always be corrected for local variation (declination) to convert to true bearings.

Grid North

• Definition: North as defined by the grid lines on a map projection (e.g., UTM, MGRS).
• Symbol: GN
• Use: Gridded map navigation, especially for large-scale land navigation and military purposes.
• Stability: Fixed per map, may differ from True North by a few degrees (grid convergence).

Comparative Table: Types of North

Bearings in Navigation

Bearings are angles that describe direction from a reference point. The reference (True, Magnetic, Grid, or Relative) must always be specified.

True Bearing (°T)

Measured clockwise from True North to a target; always used on charts and in GPS. Preferred for consistent, system-wide communication and flight/route planning.

Magnetic Bearing (°M)

Measured clockwise from Magnetic North (the direction of a compass needle). Essential for direct compass navigation but must be converted to/from true bearings for use with charts.

Relative Bearing

Measured clockwise from the current heading of the observer (000° at the nose of an aircraft or bow of a ship). Used for situational awareness—e.g., “traffic at two o’clock” or ADF radio bearings.

Grid Bearing

Measured from Grid North on a map projection; used in grid-based navigation systems.

Bearing vs Heading

• Bearing: Direction to an external object from a reference (True, Magnetic, Grid, or Relative).
• Heading: Direction in which a craft is pointed, relative to True or Magnetic North.

Declination, Variation, and Conversion

What is Magnetic Declination (Variation)?

Magnetic Declination (variation) is the angle between True North and Magnetic North at a specific location. It is expressed in degrees East (E) or West (W).

• East Declination: Magnetic North is east of True North (add to magnetic to get true).
• West Declination: Magnetic North is west of True North (subtract from magnetic to get true).

Declination changes by location and slowly shifts over time. Always use current values from chart margins or online tools.

Example Declinations (2024)

Converting Between Bearings

Key Formulas

• True Bearing (°T) = Magnetic Bearing (°M) + Declination (add East, subtract West)
• Magnetic Bearing (°M) = True Bearing (°T) - Declination
• Grid Bearing (°G) = True Bearing (°T) + Grid Convergence

Examples

1. Magnetic to True: 120°M, 5°E declination → 120° + 5° = 125°T
2. Magnetic to True: 050°M, 7°W declination → 050° - 7° = 043°T
3. True to Magnetic: 210°T, 10°E declination → 210° - 10° = 200°M

Practical Mnemonic

• “East is least, West is best” (subtract east, add west when going from magnetic to true).

Practical Use of True Bearings

Taking a True Bearing from a Map

1. Identify your position and the target on the map (which is oriented to True North).
2. Draw a line between them.
3. Use a protractor to measure the angle clockwise from the north reference line (meridian) to your line—this is the true bearing.

Taking a True Bearing in the Field

Using a Compass with Declination Adjustment

Set the local declination; sight the target and read the true bearing directly.

Using a Standard Compass

1. Sight the target, read the magnetic bearing.
2. Add/subtract declination to obtain the true bearing.

Use Cases

Marine Navigation

Plot bearings from compass readings (magnetic), convert using local declination, and transfer to nautical charts (true).

Aviation

All routes, airways, and ATC instructions use true bearings. Pilots convert compass (magnetic) headings to true for accurate navigation.

Land Navigation

Hikers and orienteers convert between map (true/grid) and compass (magnetic) bearings to stay on course.

Step-by-Step: Map to Field

1. Plot true bearing on the map.
2. Check map margin for local declination.
3. Convert true to magnetic bearing.
4. Set the magnetic bearing on your compass.
5. Orient compass and proceed along the bearing.

Step-by-Step: Field to Map

1. Take magnetic bearing to landmark.
2. Convert to true bearing by adding/subtracting declination.
3. Plot the bearing from your location on the map.

Common Mistakes and Best Practices

Common Mistakes

• Omitting Reference: Failing to specify whether a bearing is true, magnetic, or grid can lead to critical errors.
• Outdated Declination: Using old declination values may cause navigational drift.
• Incorrect Compass Adjustment: Not setting or applying declination properly can misalign navigation.

Best Practices

• Always specify the north reference (T, M, or G) when giving or recording bearings.
• Regularly update declination values from reliable sources.
• Use the conversion formulas and double-check calculations, especially in high-variation areas.
• When in doubt, consult map legends and chart marginalia for the correct references and values.

Summary

True bearing is the gold standard for precise, consistent navigation. By measuring clockwise from True North, it provides a reference immune to magnetic drift or map projection quirks. Mastery of true bearings, magnetic variation, and conversion techniques ensures safe and accurate journey planning for aviators, mariners, and land navigators alike.

For modern navigation, always:

• Know your north references.
• Apply correct corrections.
• Communicate bearings with their reference (T, M, or G).
• Keep up-to-date with local declination values.

Understanding and using true bearings is essential for anyone committed to safe and accurate navigation—whether by land, sea, or air.