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.
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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 line shapefile shows lines of equal annual change (secular variation) in the vertical component of the total field intensity of the Earth's ma... 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.
2010. National Geophysical Data Center. This line shapefile shows lines of equal vertical intensity of the Earth's magnetic field, derived from the International Geomagnetic Reference Fie... National Atlas of the United States.
1999. Geological Survey (U.S.). This line shapefile portrays the major roads in the United States, Puerto Rico, and the U.S. Virgin Islands. The file was produced by joining the i... Geological Survey (U.S.).
1856. Graham, J. D. (James Duncan), 1799-1865, O'Donoghue, John, 1946-, and United States. Army. Corps of Topographical Engineers. The soundings are in feet & decimals of a foot. "Accompanying Lt. Colonel J.D. Graham's annual report (no. 161) to the Chief Topographical Engineer...
1915. Shows locations of school houses, churches, farms, and Bad River Indian Reservation; also shows Soo Line railroad and part of Chequamegon Bay.; "La... Minneapolis, St. Paul and Sault Ste. Marie Railway Co (Minneapolis, Minn).