In 2005, there were twenty agglomerations of more than 10 million inhabitants whereas there were only two in 1950 and three in 1975. Fifteen of these cities are in developing countries. These cities alone account for 9 % of the world's population. The largest is Tokyo with 35 million inhabitants and the 9 other largest megacities are Mumbai (or Bombay) and Mexico with 21 million inhabitants, Sao Paulo -20 million, New York -19 million, Delhi -18 million, Shanghai -17 million and finally, Calcutta, Dhaka and Jakarta with 16 million inhabitants. (1)
The fabric of society of large cities tends to merge to create huge « conurbations ». Hence, the Tokaido corridor around Tokyo and Osaka could represent over 80 million inhabitants whilst the North-East corridor, between Washington, New York and Boston has 55 million inhabitants. It is often hard to draw the precise line between a city and an agglomeration.