Lower Manhattan (or downtown Manhattan) is the southernmost part of the island of Manhattan, the main island and center of business and government of the City of New York. Lower Manhattan or "downtown" is defined most commonly as the area delineated on the north by 14th Street, on the west by the Hudson River, on the east by the East River, and on the south by New York Harbor (also known as Upper New York Bay). When referring specifically to the lower Manhattan business district and its immediate environs, the northern border is commonly designated by thoroughfares approximately a mile-and-a-half south of 14th Street and a mile north of the island's southern tip: Chambers Street from near the Hudson east to the Brooklyn Bridge entrances and overpass. Two other major arteries are also sometimes identified as lower Manhattan's northern border: Canal Street, roughly half a mile north of Chambers Street, and 23rd Street, roughly half a mile north of 14th Street. The lower Manhattan business district forms the core of the area below Chambers Street. It includes the Financial District—often referred to as Wall Street, after its primary artery—and the site of the World Trade Center. At the island's southern tip is Battery Park; City Hall is just to the north of the Financial District. Also south of Chambers Street are the planned community of Battery Park City and the South Street Seaport historic area. The neighborhood of TriBeCa straddles Chambers on the west side; at the street's east end is the giant Manhattan Municipal Building. North of Chambers and the Brooklyn Bridge and south of Canal Street lies most of New York's oldest Chinatown neighborhood. Many court buildings and other government offices are also located in this area. The Lower East Side neighborhood straddles Canal. North of Canal and south of 14th Street are the neighborhoods of SoHo, the Meatpacking District, Greenwich Village, Little Italy, Nolita, and the East Village. Between 14th and 23rd streets are lower Chelsea, Union Square, the Flatiron District, Gramercy, and the large residential development Peter Cooper Village—Stuyvesant Town. The lower Manhattan business district is the fourth largest central business district in the United States, after Midtown Manhattan, Chicago's Loop, and Washington, D.C. The area was previously the third largest CBD. Lower Manhattan fell to fourth place due to the district's loss of the World Trade Center, which contributed over 16 million square feet of office space to the area. The square footage lost in the September 11, 2001 terrorist attacks was equivalent to the office space then in the entire city of Cincinnati. It is expected that the district will regain its third place ranking after the construction of the Freedom Tower, which is planned to yield close to the original center's square footage of rentable commercial space, and the construction of new headquarters for financial firm Goldman Sachs.