Courtesy of John Hillhouse, USGS The intensity and structure of the Earth's magnetic field are always changing, slowly but erratically, reflecting the influence of the flow of thermal currents within the iron core. This variation is reflected in part by the wandering of the North and South Geomagnetic Poles. Because a wide range of commercial and military navigation and attitude/heading systems are dependent on models of the magnetic field, these models need to be updated periodically. The magnetic field's strength and direction and their rates of change are predicted every 5 years for a 5-year period.

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This map was obtained from an edition of the National Atlas of the United States. Like almost all works of the U.S. federal government, works from the National Atlas are in the public domain in the United States. Online access: NationalAtlas.gov | 1970 print edition: Library of Congress, Perry-Castañeda Library čeština | Deutsch | English | français | Bahasa Indonesia | italiano | македонски | മലയാളം | sicilianu | 中文 | 中文（简体）‎ | 中文（繁體）‎ | +/−