Part of the "Megastructures: The Visual Encyclopedia" book project, on sale now at http://www.neilblevins.com/megastructures/megastructures.htm
An Arcology would be a densely populated habitat that would be self-contained and self-sustaining. It would create all of its own power, food, air, water, climate, and waste recycling, and would not require goods or services from an outside source to survive.
The name “Arcology” comes from the combination of the words “architecture” and “ecology.” The term was first coined in 1969 by architect Paolo Soleri, although the idea has been explored by a number of architects and scifi writers since the early 1900s. One example of an Arcology would be the classic science-fiction domed city. Another Arcology design would be built into the side of a mountain, like an enormous anthill.
An Arcology would provide space for residential, commercial, and agricultural systems while reducing human impact on limited natural resources. Since space is at a premium, some form of population control would likely be necessary.