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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.
2010. Geological Survey (U.S.). This polygon shapefile portrays the Public Land Surveys of the United States, including areas of private survey, donation land claims, and land gra... Geological Survey (U.S.).
2010. The Purdue historical campus map collection was scanned and georeferenced by Purdue University Libraries. The physical maps were collected as Purdu... Purdue University Libraries.