Compass Surveying

An interactive guide to the fundamental concepts of surveying with a compass, based on classic surveying principles.

Core Definitions

Compass Surveying

A branch of surveying in which the directions of survey lines are determined with a compass.

Surveyor's Compass

An instrument for determining the horizontal direction of a line with reference to the direction of a magnetic needle.

Magnetic Declination

The angle that a magnetic meridian makes with the true meridian.

Magnetic Dip

The vertical angle which the magnetic needle makes with the horizontal due to the earth's magnetic pull near the magnetic poles.

Isogonic Lines

Imaginary lines passing through points having the same magnetic declination.

Agonic Lines

Imaginary lines passing through points having zero declination.

Interactive: Magnetic Declination

Magnetic Declination is the horizontal angle between True North (geographic north) and Magnetic North (the direction a compass needle points).

30° West (-) 0° (Agonic) 30° East (+)

Note: When declination is East, Magnetic North is to the right of True North. When West, it is to the left.

True N
W E
Mag N

Bearing Systems

In compass surveying, directions of lines are usually expressed in bearings. A bearing is the acute angle a line makes with a reference meridian (usually North or South). It is typically written as: [N or S] [Angle] [E or W]. For example, N 30° E.

N S E W 45° N 45° E 30° S 30° E 60° S 60° W 20° N 20° W

Reading Bearings:

  • NE
    Northeast Quadrant

    Measured clockwise from North towards East. (e.g., N 45° E)

  • SE
    Southeast Quadrant

    Measured counter-clockwise from South towards East. (e.g., S 30° E)

  • SW
    Southwest Quadrant

    Measured clockwise from South towards West. (e.g., S 60° W)

  • NW
    Northwest Quadrant

    Measured counter-clockwise from North towards West. (e.g., N 20° W)