Much of an urban area's built environment is, for example, devoted almost exclusively to use by automobiles, buses, and trucks. Streets, parking lots, driveways, and loading ramps occupy well over half of all surface area in some parts of the city. Cooling towers for ventilation systems take up a notable amount of space, as does equipment needed to maintain telephone, electrical, water, and wastewater systems.
Most people fail to perceive how much of the urban environment is given over to machines.
Yet, machine space has tremendous effects. The concrete and asphalt used to pave streets and parking lots can change the microenvironment of the city. These changes are sometimes powerful enought to change patterns of precipitation over some cities. Machine space also adds to the impervious cover that alters the flow of rainwater through the urban ecological system. Finally, machine space can be a source of pollution as runoff and wind sweep hydrocarbons, chemicals, and other pollutants into the water and air.