What will make cities livable as millions more move to them?

In 1925 Le Corbusier, the Swiss-French architect and pioneer of modernism, suggested razing the homes, statues, and streets of much of Paris’s Right Bank. In their place, he proposed erecting 18 identical glass towers some 650 feet high, a quarter of a mile apart, divided by lawns for pedestrians and elevated highways for cars.

Le Corbusier contended that “lovers of antiques” and progressive thinkers were at war about how humans should live. A quote attributed to him leaves no doubt as to which side he was on: “Progress is achieved through experimentation; the decision will be awarded on the field of battle of the ‘new.’ ’’

This battle has long raged in and about cities, which are thought to have first formed some 6,000 years ago in what is now Iraq. We question how best to live en masse, how to coexist. The answers change with our need for security, with passing fad and fancy, and with advances in technology.

Should we live in dense urban areas with public transit and walkable amenities? In sprawling suburbs created by our infatuation with the car? In high-rises similar to those envisioned by Le Corbusier, now dotting urban districts across China? National Geographic has spent the past year exploring those questions for this month’s special coverage of cities. We sent photographers and writers across the globe to document how cities work, and don’t; from Tokyo—the planet’s largest metropolis with more than 37 million inhabitants—to Bidibidi, Uganda, essentially an instant city of more than a quarter million people, formed by refugees who’ve arrived since August 2016.

We partnered with architectural firm SOM to create a detailed representation of the city of the future. And because we are National Geographic, we also covered an urban creature that follows us no matter what city we live in: rats.

What does the future hold for cities and for the two-thirds of us who’ll live in them by 2050? While reporting our story “Rethinking Cities,” writer Robert Kunzig spent time with Jan Gehl, a Copenhagen urban designer who, Kunzig says, is “revered for his simple insights.” Let’s end with one: Gehl’s advice to be thoughtful about shaping cities, because we’re building a legacy.

“Waking up every morning and knowing that the city is a little bit better than it was yesterday—that’s very nice when you have children,” Gehl says. “Think about that … your children have a better place to live, and your grandchildren have a better place to grow up than you could when you were young. I think that’s what it should be like.”

We hope you enjoy this special issue about cities and our extended coverage on NationalGeographic.com.