Business Insider reports the world's projected fastest-growing cities based on UN population estimates are all on one continent.
The world population is expected to grow to 8.6 billion in 2030, and African metro areas are leading this growth.
Africa is growing so quickly because of its increasingly large young population, the highest of any continent.
Over 75% of its population is younger than 35.
The world's third fastest-growing city is Kampala, Uganda. It has an estimated 2020 population of 3,928,000 and is projected to grow to 7,004,000 in 2035.
Zinder, Niger, has an estimated 2020 population of 489,000 and is projected to grow to 1,065,000 in 2035.
The fastest-growing city in the world is Bujumbura, Burundi. With an estimated 2020 population of 1,013,000, it's projected to grow by 123% to 2,263,000 in 2035.