Bearing in Surveying

Definition

A bearing is a fundamental measurement in surveying that represents the direction from one point to another, expressed as an angle measured from a reference direction. Bearings are essential for establishing positions, creating maps, and conducting navigation operations across various surveying disciplines.

Types of Bearings

True Bearing

True bearing (also called astronomic bearing) is measured from true north, which aligns with the Earth's rotational axis. This bearing remains constant regardless of location and is determined through astronomical observations. True bearings are used as the reference standard in surveying.

Magnetic Bearing

Magnetic bearing is measured from magnetic north, the direction indicated by a compass needle. This type of bearing varies with location and time due to the Earth's magnetic field variations. Magnetic declination—the angle between true north and magnetic north—must be considered when converting between magnetic and true bearings.

Grid Bearing

Grid bearing is measured from grid north on a map projection system. Different map projections have different grid north directions, making grid bearings essential for large-scale surveying projects and coordinate system applications.

Measurement Systems

Whole Circle Bearing (WCB)

Whole circle bearing measures angles from 0° to 360° in a clockwise direction from north. This system is commonly used in modern surveying because it provides a unique bearing for any direction and simplifies calculations.

Quadrant Bearing

Quadrant bearing (also called bearing and distance) divides the compass into four quadrants, measuring angles between 0° and 90° from either north or south toward east or west. While less common in contemporary surveying, it remains useful in traditional navigation.

Applications in Surveying

Bearings are critical for:

Boundary Definition: Establishing property lines and legal descriptions

Traverse Surveys: Measuring angles and distances in sequential measurements

Positioning: Determining precise locations of points in the field

Map Creation: Orienting surveyed data on maps and plans

Construction Layout: Guiding construction projects with accurate directional reference

Measurement Methods

Bearings are determined using various instruments:

Compass: Provides magnetic bearing readings, suitable for reconnaissance work and preliminary surveys.

Theodolite/Transit: Measures angles with high precision, allowing calculation of bearings when combined with a known reference direction.

GPS/GNSS: Provides precise positioning data that can be converted to bearings between any two points.

Total Station: Combines angle and distance measurement, calculating bearings electronically.

Corrections and Conversions

Surveyors must account for:

Magnetic Declination: The difference between true and magnetic north varies by location and changes annually

Convergence of Meridians: In large surveys, grid north may differ significantly from true north

Bearing Adjustments: Corrections applied during traverse closures and coordinate transformations

Modern Surveying Practices

Contemporary surveying increasingly relies on GPS and geodetic systems that provide coordinates, from which bearings are calculated electronically. However, traditional bearing measurements remain important for field verification and understanding survey data.

Conclusion

Bearings represent the fundamental language of direction in surveying. Whether measured from true, magnetic, or grid north, accurate bearing determination is essential for successful surveying projects, from small boundary surveys to large-scale infrastructure development. Understanding bearing types, measurement methods, and necessary corrections ensures professional surveying practice and reliable spatial data.