A megacity is usually defined as a metropolitan area with a total population in excess of ten million people. A megacity can be a single metropolitan area or two or more metropolitan areas that converge. The terms conurbation, metropolis and metroplex are also applied to the latter. As of 2013, there are 24 megacities in existence according to the Population Reference Bureau. The largest of these are the metropolitan areas of Tokyo, Delhi, Mexico City, New York and Shanghai: each of these has a population in excess of 20 million inhabitants. Tokyo is the largest metropolitan area, while Shanghai is the largest city proper.