Healthy people, healthy cities, healthy economies

Because the growth of these cities has been accelerated and magnified by productive technologies, rapid internal migration, and high net reproduction rates, many have reached unprecedented sizes at breathless speed. Indeed, all but three of the world's 20 largest cities are in emerging markets.

Many forecasts suggest that by 2030, the four largest emerging-market economies will have overtaken the G-7 in combined size, and that by 2050, today's emerging-market economies will represent more than half the global economy and an even larger share of the world's population. These forecasts all assume that economic growth will be generated in cities.