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Start Over You searched for: Year 2010 Remove constraint Year: 2010 Place Massachusetts Remove constraint Place: Massachusetts Subject Geomagnetism--Secular variations Remove constraint Subject: Geomagnetism--Secular variations

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2010. National Geophysical Data Center. This map layer shows isoporic lines (lines of equal annual change, or secular variation, in the declination of the Earth's magnetic field), derived... National Atlas of the United States.