The direction of one point relative to another, measured as an angle from north.

Bearing in Surveying

Bearing is a fundamental concept in surveying that describes the direction from one point to another, expressed as an angle measured from a reference direction, typically north. It is essential for establishing locations, mapping terrain, and conducting precise measurements in the field.

Definition and Purpose

A bearing represents the horizontal angle between a reference meridian (usually true north or magnetic north) and a line connecting two survey points. Bearings are used to describe the orientation of survey lines, property boundaries, and geographical features. They provide a standardized method for communicating directions that is universally understood by surveyors and engineers.

Types of Bearings

True Bearing (Absolute Bearing): Measured from true north, the geographic north pole. This is the most accurate and consistent method.

Magnetic Bearing: Measured from magnetic north, which varies depending on location and changes over time due to magnetic declination. This type is useful in field work when using magnetic compasses.

Arbitrary Bearing: A bearing system established on-site without reference to true or magnetic north, sometimes used for local surveys.

Bearing Notation

Bearings are expressed in several formats:

Full Circle Bearing: Measured clockwise from north (0° to 360°)

Quadrant Bearing: Expressed as an angle from either north or south toward east or west (e.g., N45°E means 45° east of north)

Decimal Degrees: Using decimal notation (e.g., 045.50°)

Measurement and Calculation

Bearings are measured in the field using:

Magnetic Compass: Practical for preliminary surveys and field orientation

Theodolite/Transit: Provides precise angular measurements

GPS and Total Stations: Modern instruments that determine bearings electronically

Calculations may involve converting between bearing systems, adjusting for magnetic declination, and determining bearings between points using coordinates.

Applications

Bearings are critical in:

Property Surveys: Defining boundary lines and property descriptions

Engineering Surveys: Laying out construction projects and infrastructure

Cadastral Mapping: Establishing and maintaining land records

Navigation: Determining routes and directions in the field

Coordinate Calculations: Converting between bearings and coordinate geometry

Magnetic Declination

The angle between true north and magnetic north is called magnetic declination. This varies by location and changes annually. Surveyors must apply corrections to magnetic bearings to obtain true bearings, or vice versa. Historical magnetic declination data helps in verifying older surveys.

Back Bearing

The back bearing is the bearing in the opposite direction. For a bearing of N45°E (045°), the back bearing would be S45°W (225°). Back bearings are used to verify measurements and ensure consistency in survey work.

Modern Considerations

While traditional compass bearings remain important, modern surveying increasingly relies on GPS and electronic total stations that provide precise directional data. However, understanding bearing concepts remains essential for interpreting historical documents, field verification, and communicating survey results.

Accurate bearing measurements are foundational to professional surveying practice and ensure that survey data is reliable and reproducible.