If it hasn't happened already, it will happen soon. There will be more people living in cities than outside of them. As human population numbers increase, so do the number of city dwellers, because the chances of getting an education, getting a job, and getting ahead are still better in cities than in rural areas. By the year 2000, over 20 cities will have populations over 10 million, and some of these megacities will be pushing 30 million.
Cities govern humanity's relationship with nature.
Because of their high population density, they can be huge consumers of resources and producers of waste in their local bioregion. Because of their concentration of skills, information, and technological productivity, they form the linkages between their own and other bioregions, controlling the exchange of resources, and even waste between these regions. So, any serious attempt to create sustainable societies will have to involve cities. Sprawl - Build up, not out, integrate groceries, drug stores and hardware stores into neighborhood plans, develop close to public transportation and other city services, include green space, and make it walkable. Nature - Bring the countryside into the city, use local plants, encourage and manage wildlife in urban spaces, save or create wild parks as well as manicured parks, get people outside.