New York City is one of the largest cities in the world, and it is segmented into boroughs for various reasons. A borough is a unique form of government which administers the five fundamental constituent parts that make up the consolidated city. It differs significantly from other borough forms of government used in other parts of the Tri-State Region and elsewhere in the United States. Technically, under New York Law, a "borough" is a municipal corporation that results whenever a county is merged with the cities, towns and incorporated villages that are located within the County.
New York City is often referred to collectively as the "Five Boroughs". This term is used to refer to New York City as a whole unambiguously, avoiding confusion with any particular borough or with the greater metropolitan area. It is often used by politicians to counter a focus on Manhattan and to place all five boroughs on an equal standing. The term "Outer Boroughs" refers to all the boroughs excluding Manhattan, even though the geographic center of the city is in Brooklyn.
All boroughs were created in 1898 during consolidation, when the city's current boundaries were established. The Borough of The Bronx was originally those parts of New York County that had been previously ceded by Westchester County, until Bronx County was created in 1914. The Borough of Queens originally consisted of the western part of Queens County, until Nassau County was created out of the three eastern towns in 1899. The Borough of Staten Island was officially the Borough of Richmond until the name was changed in 1975 to reflect its common appellation.
Each borough is represented by a Borough President and has, with the exception of Manhattan, a borough hall (the same functions, and others, reside in the Manhattan Municipal Building). Since the abolition of the Board of Estimate in 1990 (due to a 1989 ruling of the U.S. Supreme Court ) the Borough President now has minimal executive powers, and there is no legislative function within a borough. Most executive power is exercised by the Mayor of New York, and legislative functions are the responsibility of the members of the New York City Council. Because they are counties, each borough also elects a District Attorney, as does every other county of the state. Some Civil Court judges are also elected on a borough-wide basis, although they are generally eligible to serve throughout the city.
Marble Hill, a small enclave that is physically located on the mainland, and that appears to be part of the Bronx, is actually part of Manhattan. After an increase in ship traffic in the 1890s, the Army Corps of Engineers constructed the Harlem River Ship Channel. This rendered Marble Hill an island bounded by the canal to the south and the original course of the Harlem River to the north. The old river channel was filled in 1914, linking Marble Hill to the North American mainland. A subsequent agreement between the respective Borough Presidents decreed that this neighborhood would henceforth be deemed to be part of the Borough of the Bronx. However, the agreement was never enacted into law by the legislature, so this enclave remains part of New York County.
While there are only five boroughs, a number of areas near and far have been rhetorically identified as New York City's "Sixth Borough". Places to which the "sixth borough" appellation have been applied include Hudson County, New Jersey ; Nassau County, New York ; the Lower East Side; Newark, New Jersey ; Philadelphia ; South Florida ; and even Israel. The only proposal to merit any formal consideration was a 1934 bill submitted by a New York City alderman which suggested merging Yonkers into New York City as a sixth borough.