New York City is located in the Northeastern United States, in southeastern New York State, approximately half way between Washington, D.C. and Boston. The location at the mouth of the Hudson River, which feeds into a naturally sheltered harbor and then into the Atlantic Ocean, has helped the city grow in significance as a trading city. Much of New York is built on the three islands of Manhattan, Staten Island, and Long Island, making land scarce and encouraging a high population density.
The Hudson River flows through the Hudson Valley into New York Bay. Between New York City and Troy, New York, the river is a estuary. The Hudson separates the city from New Jersey. The East River, actually a tidal strait, flows from Long Island Sound and separates the Bronx and Manhattan from Long Island. The Harlem River, another tidal strait between the East and Hudson Rivers, separates Manhattan from the Bronx. The city's land has been altered considerably by human intervention, with substantial land reclamation along the waterfronts since Dutch colonial times. Reclamation is most notable in Lower Manhattan, with developments such as Battery Park City in the 1970s and 1980s. Some of the natural variations in topography have been evened out, particularly in Manhattan. The city's land area is 322 mi² (831.4 km²). The highest point in the city is Todt Hill on Staten Island, which at 409.8 ft (124.9 m) above sea level is the highest point on the Eastern Seaboard south of Maine. The summit of the ridge is largely covered in woodlands as part of the Staten Island Greenbelt.