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2014. Geological Survey (U.S.). This line shapefile shows elevation contour lines for the conterminous United States. The map layer was derived from the 100-meter resolution eleva... National Atlas of the United States.
2004. Instituto Nacional de Estadística, Geografía e Informática (Mexico), Canada Centre for Mapping, and Geological Survey (U.S.). This line shapefile shows bathymetric contours with depth in metres for ocean areas covered by the extent of the North American Atlas project. Isob... Canada Centre for Mapping, Instituto Nacional de Estadística, Geografía e Informática (Mexico), and Geological Survey (U.S.).