The United States of America (USA), commonly known as the United States (U.S.) or America, is a federal republiccomposed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles (9.8 million km2), the United States is the world's third- or fourth-largest country by total area and just fractionally smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 325 million people, the U.S. is the third-most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous 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, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.
The climate of the United States varies due to differences in latitude, and a range of geographic features, including mountains and deserts. East of the 100th meridian, the climate is humid continental in the northern areas east through New England, to humid subtropical in the Gulf and South Atlantic regions.