The second half of the twentieth century saw the emergence of the urban
environment as the predominant habitat of our species. Never before have we
been able to say that the majority of the world lives in cities, but this time is
fast approaching. Not only will urbanization increase, but also urban population
will be more and more concentrated in what we now call the developing world.
By some measures the relative ratios of urban population in the developed and
developing world will be 20 percent and 80 percent respectively by the year