It’s Friday night as usual for a group of Jewish college students at 14 Aigburth Road. Outside, the sun has set on a quiet residential street. Inside, candles flicker in one corner of a spacious dining room. A dozen folding tables, graced with white tablecloths patterned with swirling silver, signal a feast to come.

Around the tables, skirt-clad girls chat while taking turns coddling two tiny, 4-month-old twins in what they call “baby tag.” In an adjoining study separated by lattice wood dividers, Rabbi Mendy Rivkin leads a dozen young men in reciting a ritual prayer.

Third in a series on changing cities

New York City’s metropolitan area became the world’s first megacity in the 1930s, when its population passed the 10 million mark. By 2015 New York City had fallen to No. 9 in a rapidly urbanizing world with 30 megacities. By 2018 there were 33 such cities, and forecasters anticipate 15 more megacities by 2035—perhaps six within the next decade. A World Bank report of a decade ago was right to pronounce urban growth “one of the most important challenges of the 21st century.”

Second in a series on changing cities

Walking along the long narrow stretch of Ochheuteal Beach on the Cambodian coast of Sihanoukville is like walking between two worlds. On one side, a small boy runs gleefully into the waves as the golden sun dips down to the ocean, the sky awash in purples and pinks. On the other, trash piles up on construction sites as the skeletons of buildings and tower cranes stretch to the sky.

First in a series on changing cities

When Pat Kelley was growing up in the 1960s, Chattanooga was still a bustling industrial town. Textile factories, chemical plants, and steam boiler manufacturers employed men and women by the thousands. As a boy, Kelley caught glimpses of fire flashing in the foundries and watched as steel mills hurled atomized carbon into the humid Southern air.

Rick Swinger has an odd hobby as a photographer. He likes to walk around his neighborhood with his camera jostling by his side, looking for disgusting things to photograph.

He doesn’t have to look very hard. Swinger has lived in Venice, an Instagram-famous beach town in Los Angeles, for 38 years. Just a block away from his two-bedroom condo resides one of the largest homeless encampments in Venice, where tents, sleeping bags, gallon-sized garbage bags, and random pieces of furniture litter the sidewalks.

Remember fun? Your nostalgic childhood memories probably involve some sort of toy on wheels: Big Wheels, roller skates, wagons, skateboards. The latest craze is scooters—for adults.