For all the mockery it's drawn, the central idea on which celebrity urbanist Richard Florida built his career was not a bad one. In 2002, the current University of Toronto business professor wrote The Rise of the Creative Class, about America's growing subset of workers who were generally educated, wealthy, and in creative professions. His book also advanced the creative class theory, which posits that cities do best not by luring companies, but by drawing these workers, and that economic development strategies should be tailored towards the latter. The book, the theory, and the phrase itself generated lots of buzz, earning Florida speaking fees and consulting gigs ever since.

While Florida's theory is likely limited for most U.S. cities, it partially explained the growth for many larger ones. Not only New York City and Los Angeles, but smaller cities like Miami, Nashville, San Diego and the Big Four in Texas thrive on a certain degree of cultural appeal. It might be more accurate to say that these intense agglomerations attract people of all classes, and that the resulting cultural growth attracts the creative class, specifically. But such talent attraction is an important feature of modern U.S. cities, and stressing that should never have been controversial.

Yet in recent years, Florida has backtracked a bit.

"I got wrong that the creative class could magically restore our cities, become a new middle class like my father's, and we were going to live happily forever after," he told the Houston Chronicle in 2016. "I could not have anticipated among all this urban growth and revival that there was a dark side to the urban creative revolution, a very deep dark side."

The dark side is the focus of Florida's latest book, The New Urban Crisis. He explains that this incoming creative class tide has benefited some communities, but divided others, creating a bifurcated, "winner-take-all" urbanism. That is, people with good educations and jobs can enjoy their cities, while those without such advantages get priced out of the best neighborhoods, reinforcing their poverty, inequality and spatial segregation. In some cases, the new gentrifiers are the very ones pushing others out.

To make his points, Florida provides lots of charts and graphs. He begins by noting the segregation, at global level, between the rock star, creative class cities like New York and London, and the many others that don't perform as well economically. But he notes that within these top cities, there is even worse stratification. In one illuminating chapter called “Patchwork Metropolis”, Florida shows maps of different metro areas that reveal the stark divides between where the creative class and service class live. Generally, the creative class lives within or just outside city boundaries, while the service class occupies suburbs. In Vancouver and Atlanta, there is a strong north-south divide, while in Austin, creatives settle to the west and the service class to the east. In Miami, creatives cluster in a tight strip along the waterfront, while service workers encompass a majority of the inland territory leading to the Everglades.

This, of course, is not news to those familiar with major cities. And however one wishes to look at it, these dynamics are about power, money--and space. The preexistence of dynamic cities--and the further creative class movement into them--has enabled the "spiky" spatial agglomerations that Florida has described previously. Meaning, certain spaces within given metros provide a concentration of jobs, wealth, culture and all the intoxicating trappings of urban life. Because these spaces are limited, and expensive, many people are left out. It's hard to imagine, for example, how every last person in Miami could live within walking distance of the beach.

And just as this problem isn't new, it isn't particularly urban; class-based spatial segregation has long defined America. But given that Florida's book is, in fact, about spatial segregation within creative class hubs that suffer from land and housing shortages, one concept goes notably under-reported. It is indeed the elephant in the room. That concept is "zoning."

More broadly, it is the land-use regulations that prevent housing supply from meeting demand, and that cordon certain income groups into set areas. Florida writes a small bit, as he has elsewhere, about these regulations and the NIMBYism that bolsters them. But rather than digging down, he uses the same vagaries and disclaimers that have become a trademark of center-left reporting on the housing issue.

“Land use deregulation by itself—though a necessary part of the solution to the New Urban Crisis—is insufficient to address the full breadth of the problem,” he asserts. And such deregulation may even be harmful. For example Houston, with its less-regulated model, has to Florida an unacceptable amount of suburban sprawl (he fails to mention that Houston's median home prices are about half of those in Portland, Seattle and Denver, and a mere fraction compared to New York City, San Francisco and Los Angeles). Then Florida outdoes himself by harping against vertical sprawl, despite the fact that skyscrapers are a defining feature of the two places he lives, Toronto and Miami.

“Extreme land use deregulation may well end up damaging our most innovative urban districts by encouraging too much vertical sprawl and turning them into deadened condo canyons.”

Now, to reiterate--Richard Florida has written a book about the evils of spatial segregation. To him, the New Urban Crisis boils down to the fact that people in east Austin, for example, live far away from the jobs in downtown and west Austin; that the service workers for center city New York must commute in from New Jersey and Connecticut; and that suburbs in general are becoming inadequate receiving grounds for the poor.

As Florida must know, this segregation is not accidental; it is the direct result of land use regulations. Many booming metros are allowing housing construction at a rate far below their population growth, causing high prices region-wide. Look closer, and it becomes clear that the "desirable" areas within these metros are their most restrictive parts. A combination of single-family zoning, height limits, preservation policies and growth boundaries have effectively formed velvet ropes around Manhattan, Hollywood, Silicon Valley and numerous similar areas. Even Houston, for all its merits, has policies encouraging restrictive covenants in some prime neighborhoods. That Florida doesn't frame these regulations as a leading cause--indeed the Manichean struggle--driving his New Urban Crisis suggests that he's unserious about solving it. That he even alludes to strengthening them suggests he's part of the problem.

And that displays the flaw behind the creative class theory up to now. The idea itself is excellent--creative class professionals enhance urban cultures and economies, and should be welcomed. But cities that have embraced them so far, such as San Francisco and Austin, have not anticipated for this by allowing the necessary new housing. And the results are predictable: wealthier professionals are fighting with poorer service-class workers over the same set neighborhoods and housing stocks--and the latter group is losing. Florida should have recognized this would happen, and become a more aggressive pro-housing advocate from the start.

But he has never really been this, and it begs the questions: what did Florida think was going to happen when the creative class occupied old-school ethnic neighborhoods, housing construction was artificially limited, and prices thus skyrocketed? Was that really his formula for cross-cultural harmony?

This doesn't mean that housing growth is a panacea for all of urban America's problems, much less those brought by the creative class. Florida suggests other good things, ranging from boosting service-class worker productivity to giving cities more autonomy from the federal government. But housing is the most important solution to what he defines as the New Urban Crisis, and one not fully addressed in this book.

[This article was originally published by Forbes.]