Related terms A true bearing is measured in relation to the fixed horizontal reference plane of true north, that is, using the direction toward the geographic north pole as a reference point, while a magnetic bearing is measured in relation to magnetic north, that is in relation to the north direction of the Earth's magnetic field lines at the given location. The latter is not the same as the direction toward the magnetic north pole due to magnetic anomalies. A grid bearing is measured in relation to the fixed horizontal reference plane of grid north, that is, using the direction northwards along the grid lines of the map projection as a reference point, while a compass bearing, as in vehicle or marine navigation, is measured in relation to the magnetic compass of the navigator's vehicle or vessel (if aboard ship). It should be very close to the magnetic bearing. The difference between a magnetic bearing and a compass bearing is the deviation caused to the compass by ferrous metals and local magnetic fields generated by any variety of vehicle or shipboard sources (steel vehicle bodies/frames or vessel hulls, ignition systems, etc.) A relative bearing is one in which the reference direction is straight ahead, where the bearing is measured relative to the direction the navigator is facing (on land) or in relation to the vessel's bow (aboard ship).
Grid bearing A grid bearing is measured in relation to the fixed horizontal reference plane of grid north, that is, using the direction northwards along the grid lines of the map projection as a reference point, while a compass bearing, as in vehicle or marine navigation, is measured in relation to the magnetic compass of the navigator's vehicle or vessel (if aboard ship). It should be very close to the magnetic bearing. The difference between a magnetic bearing and a compass bearing is the deviation caused to the compass by ferrous metals and local magnetic fields generated by any variety of vehicle or shipboard sources (steel vehicle bodies/frames or vessel hulls, ignition systems, etc.) 
R
Related terms
Grid bearing
D
A true bearing is measured in relation to the fixed horizontal reference plane of true north, that is, using the direction toward the geographic north pole as a reference point, while a magnetic bearing is measured in relation to magnetic north, that is in relation to the north direction of the Earth's magnetic field lines at the given location. The latter is not the same as the direction toward the magnetic north pole due to magnetic anomalies.
D
A relative bearing is one in which the reference direction is straight ahead, where the bearing is measured relative to the direction the navigator is facing (on land) or in relation to the vessel's bow (aboard ship).