Washington D.C is the capital of the United States, and was created to serve as a permanent national capital as permitted by the U.S. Constitution. The Washington Metropolitan Area, a part of Washington D.C, is the seventh-largest metropolitan area in the country. The centers of all three government branches are located in Washington D.C, as well as several of the nations monuments, museums, and landmarks. Washington D.C. is active in the global “green” campaign- 70% of land in Washington D.C. is controlled by the National Park Service, and in was recently named the nations “most walkable” city. Washington D.C. welcomes nearly 15 million visitors annually, making it a premiere destination for tourists year round.