New York’s rise as a tech center signals a major shift in the locus of venture-capital-fueled innovation. For a long time, high-tech start-ups have clustered in suburban office parks along freeways, places that are sometimes called “nerdistans.” But since the crisis, start-ups have taken an urban turn. San Francisco, which has fared extremely well since the crash, is a striking case in point. Over the past several years, Twitter has established its headquarters downtown, Pinterest has moved from Silicon Valley to San Francisco, and even Yahoo has created a new facility in the old San Francisco Chronicle building in the South of Market neighborhood. The legendary Silicon Valley investor Paul Graham saw this coming. “For all its power, Silicon Valley has a great weakness,” he wrote in 2006: “its soul-crushing suburban sprawl.” Today, San Francisco proper tops Silicon Valley as a center for venture-capital investment, by a wide margin. The same shift has happened in greater Boston, where venture-capital investment and start-up activity are now more concentrated in Cambridge and downtown Boston than in the suburbs along Route 128.

Knowledge centers like Houston make it plausible that once the fracking boom goes bust, other technologies will arise to produce cheap energy—and strong growth.

What’s surprising is that tech stayed in the suburbs for so long. The urbanist Jane Jacobs long ago noted how cities, with their deep wells of intellectual and entrepreneurial capital, and their density and diversity, provide ideal ecosystems for entrepreneurial innovation. Nineteenth-century Pittsburgh and Henry Ford’s Detroit were the Silicon Valleys of their time.

Suburban tech parks, of course, aren’t all about to be shuttered. Big, established companies like Google, Apple, and Facebook need the large amounts of space that their suburban campuses provide. Company shuttles will continue to run between San Francisco, where more and more workers prefer to live, and Cupertino or Mountain View. But new entrepreneurial activity is increasingly bubbling up from within the urban core.

Eh, yes and no. There's still plenty of startup activity in Silicon Valley too.