Globally, fertility rates have decreased by about half since 1960. What will happen to the economy when the world's aging population begins to retire?
That's right - nearly 4 billion people live inside the circle on this world map, including 22 of the world's 37 megacities.
Watch the economies of the United States, China, and India evolve before your eyes from 1970 until 2030 (projected).
This animation shows how the ranking for the most populous countries in the world will change over more than 100 years.
Rapid urbanization is creating a vastly different world. These maps show the world's fastest growing cities, as well as how things have chanced since 1950.
China has been at the forefront of economic growth for decades, but the Chinese growth engine is sputtering due to several factors including demographics.