Canada has diverse physical features defined by its oceans and inland seas. It is bordered by three oceans - the Pacific Ocean to the west, the Atlantic Ocean to the east, and the Arctic Ocean to the north. The Canadian Shield stretches from the Great Lakes in central Canada to the Arctic Ocean and covers half the country, containing many lakes and natural resources but sparse population. The Great Lakes and St. Lawrence River are important shipping routes connecting the central Canadian population heartland to international trade.