ABSTRACT
Over the next 30 years, most of the growth in the world’s population is expected to occur in the cities and towns of poor countries. Cities are now home to nearly half of the world’s total population and over three-quarters of the population of high-income countries. By 2020 the developing world as a whole is likely to have become more urban than rural. The changes under way are not only a matter of percentages, but also of scale. At the beginning of the twentieth century, just 16 cities in the world—the vast majority in advanced industrial economies—contained a million people or more. Today, almost 400 cities are of this size, and about three-quarters of them are in found in low- and middle-income countries.
