We need to notice who immigrates and why — they’re people we need (books that matter to me)

As of 2000, the population of Lagos, Nigeria, was roughly 7.2 million, somewhere between those of greater Philadelphia and Chicago. By 2030 it will be 24 million, nearly as large as metropolitan New York and London — combined.

Why it matters: We’re in the midst of a global megacity boom, and nowhere are cities growing faster than in sub-Saharan Africa, where the number of citydwellers will triple by 2050 to 1.3 billion. Rapid urbanization and everything that comes with it — economic opportunity, social turmoil, environmental upheaval — is reaching nearly every corner of the globe.

By the numbers…

• In 1950, 750 million people worldwide lived in cities — most of them in Europe or North America. The majority of the global population lived in rural areas until 2008.
• Now, 55% of the world’s population (4.3 billion people) lives in urban areas. That will jump to 68% (6.6 billion people) by 2050.
• Asia added 1 billion urban residents between 1950 and 2000, and another 900 million since. The continent is home to more than half of the world’s urban population and 17 of the 31 global megacities of 10 million or more people.
• Africa’s urbanization boom is just beginning. A decade ago, it had about half as many urban residents as Europe. A decade from now, it will have more. Two decades after that, in 2048, it will have twice as many.

Zoom in: Nigeria’s population is growing, and urbanizing, with staggering speed. It’s set to surpass the U.S. to become the third most populous on earth by 2050.

• There are already 8 times more Nigerians living in cities than there were in 1975. All of the country’s five largest cities are expected to roughly match Lagos’ breathtaking growth, meaning they’ll have to accommodate at least 70% more people by 2030.

Zoom out: Urbanization is also yielding cities of unprecedented size.

• As of 1975, there were three metro areas with at least 10 million people — Tokyo, New York and Mexico City. A list of the 10 largest cities at that time would have included Paris (now 25th), Moscow (22nd) and Los Angeles (21st).
• Now there are 31 such megacities, and the UN projects 10 more will join the list by 2030. All but one (Bogotá) are in Africa or Asia.
• We may soon need a new definition of megacity. There will be 14 cities with at least 20 million people — including Lagos and Kinshasa, in the Democratic Republic of the Congo — by 2030.

Why it matters: Urbanization can be a massive engine for economic growth — supplying labor, cutting transport costs and encouraging competition and collaboration. It can also put a massive strain on resources like water and housing.

Note: All population estimates and projections via the UN.