While cities have traditionally been regarded as a blight on the environment, city planning and creative uses of space are helping transform cities from part of the problem to part of the solution. Seeing as cities tend to be relatively crowded, roofs offer a good amount of unused space that cannot be found elsewhere. Often this roof space is used for solar panels or roof gardens, but another emerging use is micro wind turbines. In a recent article entitled "How to Build a Greener City," the Wall Street Journal explains that while windmills have typically been reserved for the countryside (as the vibrations they cause can rattle windows) developers have been working on micro-turbines. These small generators are more appropriately sized for roofs and are able to work with the turbulence and sudden directional shifts characteristic of city wind. Though each turbine contributes only one to three kilowatts, when installed in arrays or partnered with solar panels they can provide a significant share of a building's energy. In my hypothetical city, I would coat the tops of all  buildings in a combination of micro wind turbines and solar panels to help cut down need for other forms of energy.