Insularity of a city may seem to be immutable. Yet Manhattan urban development causes a continual change of the island. By means of six topographical pictures of the city the author describes the variations in time of the utilization and perception of insularity : what does remain from the harbour economy that made of New York City a harbour open onto the high seas and a refuge for immigrants ? However, symbolic landmarks such as the statue of « Liberty enlightening the world » and New York bay still contribute to nourrish the contemporaneous urban myths that inspire the reconstruction projects of the World Trade Center today. Manhattan is also the representative cinematographic picture of New York City. One of the priorities today to restore Manhattan insularity is to reconstruct the waterfront used in the 20th century as a traffic way including Manhattan into New York City.