Arcology
An arcology is a term used to describe a large-scale human habitate, pre-planned, and sometimes of one contiguous structure. The word "arcology" itself is a portmanteau of "architectural ecology," coined by Paolo Soleri, although the popular meaning of the term has broaded to cover several similar large-scale human habitats seen in fiction. However, they are not limited to the realm of science fiction, as several governments and private businesses are actively researching arcologies to put them into practical use as soon as 2010.
Advantages
Much like any planned city, an arcology can be built with an end result in mind, reducing costs. However, unlike most planned cities, arcologies are usual multi-story affairs, reducing travel time by adding vertical distance -- effectively dividing the distance needed to travel by the number of stories in the town. Because of this, an arcology using walkways instead of roads as the major source of travel would save. As an example An American arcology using walkways in lieu of would save thousands of dollars per person per year, not only in car maintenance fees but in gasoline and in necessary infrastructure to
There are other benefits as well. By reducing the distance between any two points in the city, public safety can be increased -- the response time for emergency services, whether police, medical, or fire, would be reduced by living in an arcology.
Additionally, arcologies do not to be singular, monolithic structures, as commonly seen in fiction; most arcologies being designed today are scalable. These smaller arcologies are designed to support a small number, but can link together by linking smaller related arcologies, creating a 'compartamentalized' arcology. A single-building arcology could support the population of a small town (5,000), and additional five-thousand-person arcologies could be built later in neighboring lots, effectively creating a ten-thousand, fifteen-thousand, or larger arcology.
The current limit of human technology and arcology design could, in theory, fit the entire population of Earth (c. 6 billion people) into an area no larger than Louisiana.
Limitations
Although arcologies have notable advantages, ther are many limitations inherant in their design. For example, unless notable advantages in hydroponics are made, no arcology could grow its own food -- and even then, foods grown outside arcologies would likely be cheaper, even with the cost of transport added in. For the time being, although an arcology could be built today, they cannot be self-sufficient.
In addition, some economists think arcologies would reduce competition. For example, if a Wal-Mart was in an arcology, it would be within walking distance of a greater number of people than a Wal-Mart in a conventional town, making it harder for smaller businesses to compete, stunting economic growth.
Aquatic arcologies
Several designs for arcologies are designed to be built on sea, not land. This was inspired by the fact that several large ships (including tankers and nuclear carriers) are already equipped to spend months or years at sea, and (theoretically) could be built for increased or indefinate sustainability for populations.
One such design, Freedom Ship, has attracted relatively high amounts of media attention and criticism. Its design, similar to a barge's but at a much larger scale, would support a permanant population of about 25'000, including schools, a casino, a mall, an airstrip, and 100 acres of open 'land' (parks and recreation areas). The completeness of the plans has attracted investors, although not enough to begin construction.