One example of a conurbation is the expansive concept of the New York metropolitan area (the Tri-state region) centered on New York City, including 30 counties spread among New York State, New Jersey, Connecticut, and Pennsylvania, with an estimated population of 21,961,994 in 2007. Approximately one-fifteenth of all U.S. residents live in the Greater New York City area, the world's most brightly illuminated urban conurbation and largest urban landmass. This conurbation is the result of several central cities whose urban areas have merged.