Manhattan is the most densely populated of the five boroughs of New York City. The borough is coterminous with New York County, an original county of the U.S. state of New York. The borough mostly consists of Manhattan Island, bounded by the East, Hudson and Harlem Rivers, but also includes several small adjacent islands and a small area on the mainland. Manhattan has been described as the economic and cultural center of the United States and is home to the United Nations Headquarters. Wall Street in Lower Manhattan is one of the financial capitals of the world, has an estimated GDP of over $1.2 trillion, and is home of both the New York Stock Exchange and NASDAQ. Manhattan's real estate market is among the most expensive in the world, and many multinational media conglomerates are based in the borough.
New York County is the most densely populated county in the United States, more dense than any individual American city. It is one of the most densely populated areas in the world, with a 2010 population of 1,585,873 living in a land area of 22.96 square miles (59.5 km2), or about 69,071 residents per square mile (26,668/km²). It is also one of the wealthiest counties in the United States, with a 2005 per capita income above $100,000. Manhattan is the third-largest of New York's five boroughs in population, after Brooklyn and Queens, and it is the smallest borough in land area.