Half of the world’s population now lives in cities, a number that will climb to 75% by the middle of the century. This development marks a radical break in human history, for humanity has until recently been overwhelmingly rural, concerned first and foremost with brute survival.

In “The Communist Manifesto,” Karl Marx referred to “the idiocy of rural life” — or so the mistranslation goes — as an enduring problem. In fact, Marx wasn’t talking about “idiocy” at all. Rather, he was referring to the isolation and stasis of rural life, and how it had long stymied creativity and the diffusion of ideas. Marx was right about the emancipating power of the city, and he would surely be pleased by our far more interconnected world. The highest expression of this interconnectedness is the sparkling network of global cities that has mushroomed during the past several decades, the main subject of “The Endless City” (Phaidon, 512 pages, $69.95), a wide-ranging survey produced by the ongoing Urban Age Project.

As you’d expect from a book produced by more than 30 contributors — among them lawyers, activists, architects, politicians, planners, sociologists, and historians — “The Endless City” runs the gamut from the dazzlingly insightful to the depressingly hackneyed. At its heart is a close look at six global cities: New York, Shanghai, London, Mexico City, Johannesburg, and Berlin. Perhaps the most entertaining aspect of the book is its use of clever metrics to show how similar and, more often, how different these cities really are — by comparing, for example, the amount of green space in New York (14%) and Berlin (35.6%), or the daily commute in London (1 hour and 24 minutes) and Mexico City (2 hours and 30 minutes).

So if these cities are so different, one has to wonder: What can they possibly have in common? Drawing on the work of Saskia Sassen, one of the book’s contributors, “The Endless City” defines a global city as a major metropolis that dominates what you might call the key command functions of the global economy. Yes, globalization means that capital and even labor are hyper-mobile, but face-to-face interaction still counts. The leadership class has to actually live somewhere, and they tend to cluster with others like themselves. Armies of hangers-on and aspiring somebodies follow, whether we’re talking about gentrifying Brooklyn or the slums of Soweto.

Deyan Sudjic of London’s Design Museum introduces each of the cities surveyed, and he deserves to be singled out for his consistently intelligent, often counterintuitive observations. Mr. Sudjic is admirably unhysterical, and his great strength is that he stresses that urban forms change over time, and that suburbia is not to be scorned.

Not all of his fellow contributors are so enlightened, and some in particular are locked in a narrow model of class antagonism. In an otherwise stimulating essay on the idea of the open city, Richard Sennett, the renowned sociologist, suggests that urban gentrification is about displacing the inner-city poor. But this overlooks the fact that cities tend to have a lot of residential volatility — people move in and out of a neighborhood all the time. When an area improves, people become less inclined to move out, but it’s not as though there is a tribe of inner-city indigenous people that has lived in, say, London’s borough of Hammersmith & Fulham since time immemorial. The irony is that Mr. Sennett presents himself as the heir of Jane Jacobs, a fierce opponent of the central planners who sought to turn untamed urban landscapes into sterile Modernist nightmares. Rather than condemn the free market as such, Mr. Sennett would be better served by explicitly championing the cause of small-scale entrepreneurs and property owners fighting against eminent domain abuse and the absurd zoning restrictions he rightly criticizes. This has relevance not only in the cities of the north, but also in the expanding metropolises of Africa and Asia, where the fight for stable property rights represents the first step toward lasting prosperity.

It is worth emphasizing that most of the new global cities are very different from, say, New York or London. Some, indeed, are scarcely recognizable as cities. Vast slums in Lagos and Dhaka now dwarf Boston and Brussels. By 2020, there will be 1.4 billion slum dwellers in the world, which is to say more slum dwellers than there are Chinese or Indians. And though Westerners tend to look on this urban frontier with dread, as a slow-motion crisis to be contained, we must remember two things: first, that New York was a pestilential hellhole until relatively recently, and second, that we have much to learn from how these strange new cities are surviving and thriving.

“The Endless City” restricts its discussion of this fast-expanding urban universe to a brief discussion of African urbanism, which is heavy on ethnographic jargon and light on substance. The section on Mexico City offers more insight, yet it is a story of the past, a middle-income city in a middle-income country that is no longer defined by explosive growth. Fortunately, it seems that a future edition of “The Endless City” will tackle Mumbai.

Mumbai is just one of many cities, New York included, that could stand to learn from London. Mr. Sudjic finds much to admire in the leadership of London’s former mayor Ken Livingstone, who embraced congestion pricing and brownfield development as paths to a greener, denser city. But in truth London’s longer-term success is rooted in its tradition of decentralized self-government. For all his outsize ego, Mr. Livingstone had far fewer powers than Mayor Bloomberg. Indeed, as Gerald Frug argues in a smart essay on local government, New York is an extreme outlier in its extreme concentration of power — it is, remarkably, more centralized than communist Shanghai. Whereas New York is divided into five powerless boroughs, real power in London is in the elected governments of its 32 boroughs, which deliver services and make planning decisions. The borough governments are more responsive to the needs of neighborhoods, and they embody the different sensibilities that prevail in different parts of town. Because the global cities of the global south are at least as diverse as London, it stands to reason that they will also resist one-size-fits-all solutions. One hopes they won’t be misruled by an overmighty City Hall located far from the slums.

Mr. Salam is an editor at the Atlantic and a fellow at the New America Foundation. He is the co-author of “Grand New Party,” which will be published by Doubleday in June.