"Everyone knows which industry dominates ... Detroit and Houston. But how many could name the capital of socks? Or medical imaging technology? Or firearms? These are among dozens of hidden capitals of vital U.S. industries, each populated by and dependent upon dozens of small companies that both compete and collaborate.

This idea of industry capitals, or "clusters," as academics call them, might seem like a quaint tourist draw for small towns, an excuse, say, for Gilroy, Calif., to throw its annual garlic festival. But they serve an important function in the economy. Overlapping businesses in the same region gain a number of advantages, drawing in more suppliers and customers along with financial institutions that understand the industry. Meanwhile, the labor pool grows to include more workers with special skills and experience."

• Virtual Reality Software -- Central Florida


• Light Aircraft -- Wichita, Kansas


• Orthopedic Surgery -- Birmingham, Alabama


• Weight-Loss Centers -- Durham, North Carolina


• Firearms -- Sturgis, South Dakota


• Cardiac Devices -- Minneapolis and St. Paul, Minnesota


• Medical Imaging Technology -- Central Massachusetts


• Helicopters -- Phoenix