1945. VMap1 is a vector digital topographic reference product developed by Natural Resources Canada (NRCan) and The Department of National Defence (DND).... Canada Centre for Mapping and Earth Observation.
2004. Instituto Nacional de Estadística, Geografía e Informática (Mexico), Geological Survey (U.S.), and Canada Centre for Remote Sensing. This polygon shapefile shows areas of permanent ice found on the North America landmass including Greenland, and also shows areas of land found wit... Geological Survey (U.S.).