Manhattan - Geography

Geography

The bedrock underlying much of Manhattan is a mica schist known as Manhattan Schist. It is a strong, competent metamorphic rock well suited for the foundations of tall buildings and the two large concentrations of skyscrapers on the island occur in locations where the formation is close to the surface. In Central Park, outcrops of Manhattan Schist occur and Rat Rock is one rather large example.

Manhattan is loosely divided into Downtown (Lower Manhattan), Midtown (Midtown Manhattan), and Uptown (Upper Manhattan), with Fifth Avenue dividing Manhattan's east and west sides. Manhattan Island is bounded by the Hudson River to the west and the East River to the east. To the north, the Harlem River divides Manhattan Island from The Bronx and the mainland United States. Several small islands are also part of the borough of Manhattan, including Randall's Island, Wards Island, and Roosevelt Island in the East River, and Governors Island and Liberty Island to the south in New York Harbor. Manhattan Island is 22.7 square miles (59 km2) in area, 13.4 miles (21.6 km) long and 2.3 miles (3.7 km) wide, at its widest (near 14th Street). New York County as a whole covers a total area of 33.77 square miles (87.5 km2), of which 22.96 square miles (59.5 km2) are land and 10.81 square miles (28.0 km2) are water.

One neighborhood of New York County is contiguous with The Bronx. Marble Hill at one time was part of Manhattan Island, but the Harlem River Ship Canal, dug in 1895 to improve navigation on the Harlem River, separated it from the remainder of Manhattan as an island between the Bronx and the remainder of Manhattan. Before World War I, the section of the original Harlem River channel separating Marble Hill from The Bronx was filled in, and Marble Hill became part of the mainland.

Marble Hill is one example of how Manhattan's land has been considerably altered by human intervention. The borough has seen substantial land reclamation along its waterfronts since Dutch colonial times, and much of the natural variation in topography has been evened out.

Early in the 19th century, landfill was used to expand Lower Manhattan from the natural Hudson shoreline at Greenwich Street to West Street. When building the World Trade Center, 1.2 million cubic yards (917,000 m³) of material was excavated from the site. Rather than dumping the spoil at sea or in landfills, the fill material was used to expand the Manhattan shoreline across West Street, creating Battery Park City. The result was a 700-foot (210-m) extension into the river, running six blocks or 1,484 feet (450 m), covering 92 acres (37 ha), providing a 1.2-mile (1.9 km) riverfront esplanade and over 30 acres (12 ha) of parks.

Geologically, a predominant feature of the substrata of Manhattan is that the underlying bedrock base of the island rises considerably closer to the surface near the midtown district, dips down lower between 29th street and Canal street, then rises toward the surface again under the Financial district. This feature is the underlying reason for the clustering of skyscrapers in the Midtown and Financial district areas, and their absence over the intervening territory between these two areas, as their foundations can be sunk more securely into solid bedrock.

Manhattan has fixed highway connections with New Jersey to its west by way of the George Washington Bridge, the Holland Tunnel, and the Lincoln Tunnel, and to three of the four other New York City boroughs—the Bronx to the northeast and Brooklyn and Queens on Long Island to the east and south. Its only direct connection with the fifth New York City borough is the Staten Island Ferry across New York Harbor, which is free of charge. The ferry terminal is located near Battery Park at its southern tip. It is possible to travel on land to Staten Island by way of Brooklyn, by using the Verrazano-Narrows Bridge.

The Commissioners' Plan of 1811, called for twelve numbered avenues running north and south roughly parallel to the shore of the Hudson River, each 100 feet (30 m) wide, with First Avenue on the east side and Twelfth Avenue in the west. There are several intermittent avenues east of First Avenue, including four additional lettered avenues running from Avenue A eastward to Avenue D in an area now known as Alphabet City in Manhattan's East Village. The numbered streets in Manhattan run east-west, and are 60 feet (18 m) wide, with about 200 feet (61 m) between each pair of streets. With each combined street and block adding up to about 260 feet (79 m), there are almost exactly 20 blocks per mile. The typical block in Manhattan is 250 by 600 feet (180 m).

According to the original Commissioner's Plan there were 155 numbered crosstown streets, but later the grid has been extended up to the northernmost corner of Manhattan, where the last numbered street is 220th Street (Manhattan). Moreover, the numbering system continues even in The Bronx, north of Manhattan, despite the fact that there the grid plan is not so regular; there the last numbered street is 263rd Street.

Fifteen crosstown streets were designated as 100 feet (30 m) wide, including 34th, 42nd, 57th and 125th Streets, some of the borough's most significant transportation and shopping venues. Broadway is the most notable of many exceptions to the grid, starting at Bowling Green in Lower Manhattan and continuing north into the Bronx at Manhattan's northern tip. In much of Midtown Manhattan, Broadway runs at a diagonal to the grid, creating major named intersections at Union Square (Park Avenue South/Fourth Avenue and 14th Street), Madison Square (Fifth Avenue and 23rd Street), Herald Square (Sixth Avenue and 34th Street), Times Square (Seventh Avenue and 42nd Street), and Columbus Circle (Eighth Avenue/Central Park West and 59th Street).

A consequence of the strict grid plan of most of Manhattan, and the grid's skew of approximately 28.9 degrees, is a phenomenon sometimes referred to as Manhattanhenge (by analogy with Stonehenge). On separate occasions in late May and early July, the sunset is aligned with the street grid lines, with the result that the sun is visible at or near the western horizon from street level. A similar phenomenon occurs with the sunrise in January and December.

The Wildlife Conservation Society, which operates the zoos and aquariums in the city, is currently undertaking The Mannahatta Project, a computer simulation to visually reconstruct the ecology and geography of Manhattan when Henry Hudson first sailed by in 1609, and compare it to what we know of the island today.