The United States of America (USA), commonly known as the United States (U.S.) or the United States, is a Federal Republic composed of 50 states, one Federal District, five major autonomous territories and various properties. With an area of 3.8 million square miles (9.8 million square kilometers) and a population of more than 325 million, the United States is the third largest country in the world (in terms of total area) and the third largest population country. The capital is Washington, D.C., and the most populous city is New York City. Forty eight states and the Federal District of the capital are contiguous, between North America and Canada and Mexico. Alaska is located in the northwest corner of North America, bordering Canada in the East and Russia across the Bering Strait in the West. Hawaii is an archipelago in the middle of the Pacific Ocean. The U.S. territory is located around the Pacific and the Caribbean and spans nine official time zones. The extremely diverse geography, climate and wildlife of the United States make it one of the 17 biodiversity countries in the world.