RURAL WORLD NOW AN URBAN ONEAmong all the Third World cities, only Shanghai boasted of a population of full five million souls in 1950. According to an estimate by the United Nations population specialists, however, there will be no less than forty-five such supercities in the poorer half of the world by the year 2005. London, meanwhile, will have fallen from the once prestigious position of being the secondlargest in the world to the extremely modest position of being number twenty-seven down the line. If current trends continue, the metropolitan area of Mexico City, today with about seventeen million people and ahead of Tokyo as the world's most populous centre, will reach twenty-six million by 2005. Sao Paulo will be right behind at twenty-four million. Life, in metropolitan areas of such immense proportions, is compressed and miserable. Already in some districts of Cairo and Djakarta, as many as two to three hundred thousand people are jammed into every single square mile. This is four times the population density of comparable towns in the West. "Stabilization of global population is still virtually a century away," writes a noted urbanologist: "Before zero population growth is achieved, therefore, cities could come to resemble insect colonies rather than human habitats."Life in such metropolitan areas