Magnetic Declination Varies Considerably Across The United States
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The magnetic needle in a compass is attracted by the magnetism of the Earth, and therefore always points to the constantly shifting Magnetic North Pole. The Geographic North Pole is static and is located about 1200 miles north of the Magnetic Pole. Maps and directions are usually oriented toward the Geographic Pole, also referred to as "True North."
Magnetic declination is the direction and amount of variation between the Magnetic Pole and True North. The amount and direction of declination depends upon how those two poles align relative to a given point on Earth. When the two poles align, declination is zero, and the line of zero declination is termed the agonic line. At points west of the agonic line, a magnetic needle will point east of true north (positive declination). At points east of the agonic line, a magnetic needle will point west of true north (negative declination). There is a pattern, but it does not follow meridians or parallels. Isogonic lines are like magnetic contour lines – they trace a path of constant magnetic declination.
