Gardeners and beekeepers are taking over urban rooftops. In his New York Times op-ed, Columbia University professor Dickson D. Despommier offers another ingenious way to bring local ingredients to the cityscape: vertical farms. "Move most farming into cities, and grow crops in tall, specially constructed buildings," he writes. His vision would include multiple floors of produce grown using hydroponic and aeroponic technologies that would use less water than conventional farms. And because these farms would be within city limits, the new definition of local might be reined in from say, 100 miles, to just around the corner.