Even if you didn’t use GPS to find your way around town today, there’s every chance it touched your life. The Global Positioning System is now integrated into almost every part of modern existence. It helps land planes, route cell phone calls, predict the weather, grow food, and regulate global finance. Our guest, Greg Milner, has written a book that traces the history of GPS. He also examines the frightening costs of our growing dependence on it. (Rebroadcast)