Manhattan business days, the influx of commuters increases this number to over 3.9 million, or more than 170,000 people per square mile (65,600/km). Manhattan has the third-largest population of New York City's five boroughs, after Brooklyn and Queens, and is the smallest borough in terms of land area. Many districts and landmarks in Manhattan are well known, as New York City received a record 62.8 million tourists in 2017, and Manhattan hosts three of the world's 10 most-visited tourist attractions in 2013: Times Square, Central Park, and Grand Central Terminal. The borough hosts many prominent bridges, such as the Brooklyn Bridge;
History of New York City (1855–1897) movement of the 1950s. Pre-war steam ferries had already made Brooklyn Heights into a bedroom community for affluent professionals on Wall Street and other urban areas. Elevated railroads, operated by the Manhattan Railway Company, and other new public transport expanded the commuter area of New York, allowing development of suburbs for commuters of more modest means in Upper West Side and other distant areas. Plans were made for subways to still more remote exurbs such as Harlem and the West Bronx. In the late 19th century, the island's schist bedrock encouraged the early skyscrapers whose successors characterize its skyline today.