2010. National Geophysical Data Center. This map layer shows isogonic lines (lines of constant declination of the Earth's magnetic field), derived from the International Geomagnetic Refer... National Atlas of the United States.
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2010. National Geophysical Data Center. This line shapefile shows lines of equal horizontal intensity of the Earth's magnetic field, derived from the International Geomagnetic Reference F... National Atlas of the United States.
2010. National Geophysical Data Center. This shapefile shows isoclinic lines (lines of constant inclination of the Earth's magnetic field), derived from the International Geomagnetic Refe... National Atlas of the United States.
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.
2010. National Geophysical Data Center. This line shapefile shows lines of equal annual change (secular variation) in the horizontal component of the total field intensity of the Earth's ... National Atlas of the United States.
2010. National Geophysical Data Center. This shapefile shows lines of equal annual change (secular variation) in the inclination of the Earth's magnetic field, derived from the Internatio... National Atlas of the United States.
2010. National Geophysical Data Center. This line shapefile shows lines of equal annual change (secular variation), in the total field intensity of the Earth's magnetic field, derived fro... National Atlas of the United States.
2010. National Geophysical Data Center. This shapefile contains isodynamic lines (lines of equal total intensity of the Earth's magnetic field), derived from the International Geomagnetic... National Atlas of the United States.
2004. Instituto Nacional de Estadística, Geografía e Informática (Mexico), Geological Survey (U.S.), and Canada Centre for Remote Sensing. This polygon shapefile shows areas of permanent ice found on the North America landmass including Greenland, and also shows areas of land found wit... Geological Survey (U.S.).
2004. Instituto Nacional de Estadística, Geografía e Informática (Mexico), Geological Survey (U.S.), and Canada Centre for Remote Sensing. This line shapefile shows the coastline, linear hydrographic features, and area hydrographic features in North America. This data set was produced ... Geological Survey (U.S.).