Cities are the most complex creations of humanity.
Envisioning alternatives within such complicated systems can boggle the mind. At the same time, a certain set of ideas informs most thinking about ecological cities, a common sense about the kinds of changes it would take to make a Green City. The prime goal is to create a system that conserves materials as much as possible, importing into the city the minimum possible amount of raw materials, especially virgin substances. This means the development of an entire ecosystem of use and production, one in which conscious planning and effort is given to using byproducts of one activity as raw materials for another. The aim is closed systems which plug holes leaking into the waste stream.