The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territories, 326 Indian reservations, and some minor possessions. At 3.8 million square miles (9.8 million square kilometers), it is the world's third- or fourth-largest country by total area. It borders Canada to the north and Mexico to the south. With a population of more than 331 million people, it is the third most populous country in the world. The national capital is Washington, D.C., and the most populous city is New York City.