Frequently Asked Question
To assist confusion about Norths in mapping
Last Updated 8 years ago
Q. To assist confusion about Norths in mapping
A. Grid North
The direction north as measured on gpMapper
True North
Direction of the North Pole from an observer on the Earth.
Magnetic North
Location in the Northern Hemisphere where the lines of force from Earth's magnetic field are vertical. This point on the Earth gradually changes its position with time.
Example:
The magnetic declination for Perth (31 57'S, 115 51'E) at 1 July 2002 is -1.6 degrees. A compass bearing of 72 degrees in Perth converts to a true bearing of 70.4 degrees [72 + (- 1.6)].
Map and compass users often require the angle between grid north and magnetic north. Grid north differs from true north by the "grid convergence". The MGA94 grid convergence for the Perth location above is -0.6 degrees. A true bearing of 70.4 degrees in Perth converts to a grid bearing of 69.8 degrees [70.4 + (-0.6)].
Grid convergence and magnetic declination are shown in diagrammatic form on some topographic maps. The signs of these values can be deduced from the diagram.
A. Grid North
The direction north as measured on gpMapper
True North
Direction of the North Pole from an observer on the Earth.
Magnetic North
Location in the Northern Hemisphere where the lines of force from Earth's magnetic field are vertical. This point on the Earth gradually changes its position with time.
Example:
The magnetic declination for Perth (31 57'S, 115 51'E) at 1 July 2002 is -1.6 degrees. A compass bearing of 72 degrees in Perth converts to a true bearing of 70.4 degrees [72 + (- 1.6)].
Map and compass users often require the angle between grid north and magnetic north. Grid north differs from true north by the "grid convergence". The MGA94 grid convergence for the Perth location above is -0.6 degrees. A true bearing of 70.4 degrees in Perth converts to a grid bearing of 69.8 degrees [70.4 + (-0.6)].
Grid convergence and magnetic declination are shown in diagrammatic form on some topographic maps. The signs of these values can be deduced from the diagram.