According to the Economist, currently, 52% of the world’s population currently live in urban areas. By 2025, this should increase to 58%. Nearly all this growth will take place in emerging-market economies, particularly Asia, as migrants from the countryside move in search of jobs.
Today, these emerging-market city-dwellers account for more than 60% of the world’s GDP growth.
In the past 15 years Delhi’s population has grown by 10m; it will add another 6m (a Miami's worth) in the next 15.
Over the next two decades urban areas in emerging economies will account for about two-thirds of worldwide infrastructure spending. Most will go on building homes. China and India together will add 16 trillion square meters of housing over this period, to accommodate half a billion extra people.
On a related note, here is an interesting video about India's growth.