2003. USGS National Center for EROS. The North America Shaded Relief data were derived from the GTOPO30 elevation data. GTOPO30 is a global digital elevation model (DEM) with a horizon... National Atlas of the United States.
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2005. Reed, John Calvin, Jr. 1930- and Bush, Charles A. This line shapefile contains text labels (for display purposes) of geologic lines coverages for Alaska, Hawaii, Puerto Rico and the U.S. Virgin Isl... Geological Survey (U.S.).
2005. Reed, John Calvin, Jr. 1930- and Bush, Charles A. This line shapefile contains lines with labels and tags for major geologic units in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands. In add... Geological Survey (U.S.).
2005. Reed, John Calvin, Jr. 1930- and Bush, Charles A. This polygon shapefile contains polygon boundaries, tags and labels for major geologic units in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Isl... Geological Survey (U.S.).
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.
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.