The United States is a constitutional federal republic country comprised of a federal district, which is the Washington, D.C., and fifty states, two of which –Alaska （阿拉斯加）and Hawaii（夏威夷） – are separated from the continental United States.

The total land area of the country is about 9.37 million square kilometers. This number may vary due to different means of calculation, including whether to count in the water territories. However, according to the land area, it’s the world’s fourth largest country in size after Russia, Canada and China. The mainland covers a distance of some 4500 kilometers from east to west and about 2700 kilometers from south to north. The USA has a long coastline of 19,924 kilometers, which makes it one of the countries with the longest coastlines in the world.

The United States includes 50 states and a federal district of Columbia. For many years,there were 48 states, and then in 1959, Alaska and Hawaii became the 49^thand 50^th states. The two newest states are separated from the continental United States. Alaska is in the northwest corner of North America,bordered by Canada to the east and across the Bering Strait（白令海峡） from Russia to the west. Hawaii is an archipelago（群岛）in the central Pacific Ocean. Among the states in the US, Alaska is the largest in area and Rohde Island（罗德岛州） is the smallest. On the mainland, Texas（德克萨斯） is the largest state.

    The United States also has overseas territories with varying levels of independence,such as Puerto Rico （波多黎各）and the U.S. Virgin Islands （美属维京群岛）in the Caribbean Sea（加勒比海）, and the inhabited territories of Guam（关岛） in the Pacific Ocean, along with a number of uninhabited island territories.