Places with more than 10 million residents — known as megacities — are becoming more common as people from rural areas migrate to urban ones.

Why it matters: The benefits of megacities — which include opportunities for upward mobility and higher wages — can be offset by their negatives, like the fact that they're breeding grounds for COVID-19.

What's happening: Urbanization is proceeding rapidly, with more than half of the world's population now living in cities, according to Visual Capitalist, an online publisher aimed at investors.

• Cities like Delhi and Shanghai are growing particularly fast.
• Tokyo — population 38 million — has the most people, but declining birth rates and an aging population could mean that Delhi surpasses it by 2028.
• By 2035, Bangalore (India) and Lahore (Pakistan) are expected to replace Tianjin (China) and Buenos Aires (Argentina) in the top 20 list, Visual Capitalist said.

Where it stands: The U.S. has two megacities — New York and Los Angeles — but only New York cracked the global top 20, according to Macrotrends, a research platform for investors that published side-by-side rankings of the most populous cities in the U.S. and the world.

• Rounding out the top 10 in the U.S.: Chicago, Houston, Dallas-Fort Worth, Miami, Atlanta, Philadelphia, Washington, D.C. and Phoenix.

The bottom line: "The world is a crowded place, with human population expected to reach 9 billion by mid-century," says National Geographic, which published this fun interactive of major megacities.