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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.
2002, 2003, and 2004. Geological Survey (U.S.). This point shapefile portrays major dams of the United States, including Puerto Rico and the U.S. Virgin Islands. The map layer was created by extr... Geological Survey (U.S.).
2006. Rawson, Peg. This point shapefile depicts major dams in the United States, including Puerto Rico and the U.S. Virgin Islands. The map layer was created by extra... United States. Bureau of Transportation Statistics.
2013. Waterborne Commerce Statistics Center (U.S.) and United States. Bureau of Transportation Statisticsf. This point shapefile depicts ports politically defined by port limits or USACE projects, excluding non-USACE projects not authorized for publicatio... United States. Bureau of Transportation Statistics.
1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, and 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.).
1851. Center for Spatial and Textual Analysis. This layer is a georeferenced raster image of a map of the United States, Canada, Mexico, Central America, and the West India Islands, with portion... Stanford Digital Repository.
1947, 1948, 1949, 1950, 1951, 1952, 1953, 1954, 1955, 1956, 1957, 1958, 1959, 1960, 1961, 1962, 1963, 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, and 2000. Schultz, Kenneth A. This polygon shapefile represents areas that were the subject of interstate territorial disputes between 1947 and 2000. The disputed areas referenc... Stanford Digital Repository.