Waste-to-Energy (WTE) or energy-from-waste is the process of generating energy in the form of electricity and/or heat from the incineration of waste. In the U.S., some cities primarily in the northeastern and mid-Atlantic, burn part of their municipal solid wastes. Hemmed in by major population centers, landfill space in these areas is at a premium, so burning wastes to reduce their volume and weight makes sense. Combustion reduces the volume of material by about 90 percent and its weight by 75 percent. The heat generated by burning wastes has other uses, as well, as it can be used directly for heating, to produce steam or to generate electricity.