|The most important geomagnetic fact to remember, the earth’s magnetic field is neither uniform, stationary, nor perfectly aligned with the planet’s poles. True north can be determined with a compass reading plus/minus (as appropriate) the location’s magnetic deviation. Magnetic deviation (also called magnetic declination, magnetic variation, or compass variation) is the angle between the north compass (magnetic) heading and the heading to true (geographic) north. For absolute accuracy, you can call your local airport control tower to find the magnetic correction value for your area; this value can also be found on local maps though many maps ommit this value. The following maps are also called isogonic maps.