The United States of America, commonly referred to as the United States (U.S.) or America, is a constitutional federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions. Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The state of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea. Nine time zones are covered. The geography, climate and wildlife of the country are extremely diverse.
At 3.8 million square miles (9.8 million km2) and with over 324 million people, the United States is the world's fourth-largest country by total area (and fourth-largest by land area) and the third-most populous. It is one of the world's most ethnically diverse and multicultural nations, and is home to the world's largest immigrant population. Urbanization climbed to over 80% in 2010 and leads to growing megaregions. The country's capital is Washington, D.C. and its largest city is New York City; the other major metropolitan areas, all with around five million or more inhabitants, are Los Angeles, Chicago, San Francisco, Boston, Dallas, Philadelphia, Houston, Miami, and Atlanta.