Manhattan () is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state of New York. Located near the southern tip of New York State, Manhattan is based in the Eastern Time Zone and constitutes both the geographical and demographic center of the Northeast megalopolis and the urban core of the New York metropolitan area, the largest metropolitan area in the world by urban landmass. Over 58 million people live within 250 miles of Manhattan, which serves as New York City’s economic and administrative center, cultural identifier, and the city’s historical birthplace. Residents of the outer boroughs of New York City often refer to Manhattan as "the city". Manhattan has been described as the cultural, financial, media, and entertainment capital of the world, is considered a safe haven for global real estate investors, and hosts the United Nations headquarters. Manhattan also serves as the headquarters of the global art market, with numerous art galleries and auction houses collectively hosting half of the world’s art auctions. Situated on one of the world's largest natural harbors, the borough consists mostly of Manhattan Island, bounded by the Hudson, East, and Harlem rivers along with several small adjacent islands, including Roosevelt, U Thant, and Randalls and Wards Islands. Manhattan additionally contains the small neighborhood of Marble Hill on the U.S. mainland, which is separated from Manhattan Island by the Harlem Ship Canal and was later connected using landfill to the Bronx. Manhattan Island is divided into three informally bounded components, each cutting across the borough's long axis: Lower, Midtown, and Upper Manhattan. Anchored by Wall Street in the Financial District of Lower Manhattan, New York City has been called both the most economically powerful city and the leading financial center of the world, and Manhattan is home to the world's two largest stock exchanges by total market capitalization, the New York Stock Exchange and Nasdaq. Many multinational media conglomerates are based in Manhattan, and the borough has been the setting for numerous books, films, and television shows. Manhattan real estate is among the most expensive in the world, with the value of Manhattan Island, including real estate, estimated to exceed US$3 trillion in 2013; median residential property sale prices in Manhattan approximated US as of 2018, with Fifth Avenue in Midtown