The economic rise of China, India and Southeast Asia has prompted talk of an Asian century, reflecting a rebalancing of power from West to East.

Another global trend, however – the growth of cities – promises to be just as transformational.

In 1950, more than two thirds of the world’s population lived in rural areas. By 2050, forecasters predict the ratio will have reversed, with just one third of people living in the countryside, and two thirds living in a city.

The halfway mark was passed in 2007, the first year in history when there were more people in cities than the countryside, according to UN estimates.

Asia – already home to more than half of the world's city-dwellers, despite relatively modest urbanization today – should cross over in about five or so years’ time.

The world’s rural population, currently standing at around 3.4 billion according to the UN’s World Urbanization Prospects report, is still growing, albeit slowly. Sometime after 2020, the number will start to decline.

By contrast, the world’s urban population has expanded dramatically, from 746 million in 1950 to 3.9 billion today.

By 2050, 2.5 billion more should join them, predominantly in Asia and Africa. Over a third of that growth will come from three countries: China, India and Nigeria.

More mega-cities

The urban century is also notable for the rise of the mega-city – powerful economic dynamos accommodating more than 10 million people. In 1950, the world had two: New York and Tokyo. In 2014, the UN counted 28, including 16 in Asia. By 2030, UN forecasters estimate there will be 41.

The fastest growth however is taking place in smaller cities, mainly in Asia and Africa. While about one in eight of the world’s urban residents live in a mega-city today, almost half live in smaller urban centers of less than 500,000 people.

Some cities meanwhile, mostly in mature Asian and European markets, are shrinking, as developing markets power the urban drive.

In some ways, urbanization is good news for governments and people. It is cheaper, and less environmentally damaging to provide basic services such as housing, electricity, sanitation and water to urban populations. City dwellers tend to be healthier, with access to larger and more diverse labor markets.

Nonetheless, rapid urban growth poses daunting challenges as well as opportunities, further heightening the social and economic trends that are reshaping the world.