The United States of America is a federal republic on the continent of North America. It is the third largest country in the world after Russia and Canada. The estimated U.S. population for the year 2008 is 303,745,311 third in the world behind China and India. The United States consists of 48 contiguous states and the noncontiguous states of Alaska and Hawaii. In addition, the United States includes a number of outlying areas, such as the Commonwealth of Puerto Rico and the Virgin Islands of the United States, which are located on the Caribbean Sea, and the islands of American Samoa and Guam, located in the Pacific Ocean. The national capital is Washington, D.C., located along the banks of the Potomac River between the states of Maryland and Virginia.