The growth of large cities and metropolitan areas has been one of the most remarkable demographic stories of past decades. The map depicts the 30 largest metropolitan area in 2011
with the circles proportional to their population size. Cities of 10 million or more are often referred to as “mega-cities.” In 1950, 117 million people lived in the top 30 metros but that
number rose to 426 million by 2011. In 1950, 19 of the top 30 cities were in industrialized countries. By 2011, that number had shrunk to eight. In 1950, Delhi was not even in the top 30
but it is now second behind only Tokyo. Such phenomenal growth is usually due to rural-urban migration as migrants seek a better life in cities.