"Milespires and the Rebirth of the Environment"
(c) 2007, 2011 by Jordan S. Bassior
Here's the way I envision the residential patterns of about 100-200 years hence.
Most people live in very large structures -- what has been termed "arcologies" -- which are big enough to contain their own major utilities. The typical design of such an arcology would be a tower, perhaps a mile high (*) and a mile and a half deep: the reason being to minimize the footprint of the building on the land.
Each tower is powered by its own generator: depending on the era and technological assumptions either a fission or fusion reactor, which is built into the lower sub-basements. It may or may not be connected to the grid, depending on era, technological assumptions, and geography. It also contains its own waterworks, etc.
Because most everyday goods are by this time made by programmable fab-printers, and because a tower this large with that much energy can fairly easily synthesize its own food, there is not much need for bulk deliveries. Consequently, the tower doesn't need much in the way of cargo support: what's needed can generally be flown in.
Each resident of the arcology has a very large amount of space. Even if we assume that none of the subterranean part of the tower is fit for normal residential use, and that half of the above-ground part of the tower is reserved for structural systems (such as girders), support systems (such as elevators) and commerce, that leaves about 2500 feet of tower for residential purposes: at 20 feet per floor(allowing split-level apartments) if the mile-high tower is roughly a quarter-mile by a quarter mile, there will be 125 residential floors, each comprising about 1.5 million square feet, for a total of about 187 million square feet of living space (and this isn't a very efficient tower design, I'm making very conservative assumptions). If 10 thousand people live in the tower, that's 18,700 square feet of 20-foot vertical room per person, or the equivalent of a two-story house 187 by 100 feet, which I think most people would find quite ample! (**)
Now note: this is the equivalent of a small town, but its area footprint is only a quarter-mile on a side, which is more like the extent of a small town's business district. And it does not require an extensive road and rail network to support it, because physical commuting is done by aircar and most goods transport by airtruck. It recycles most of its gases and liquids, and its power source is clean. Its ecological impact (aside from its shadow, which moves as the day goes on) is far less than that of a modern-day 10,000-person town.
These milespires might be all over the place, but separated by miles of intervening distance, providing ample room both for air traffic andfor ecological purposes. Most of the ground between them, including abandoned old-style towns, might become a wilderness preserve -- in North America, much of it a vast forest or prairie, into which the Pleistocene megafauna would be allowed to return. In other places, other megafaunal populations could be brought back.
With far less geographical footprint and an economy based on relatively non-polluting energy sources, means of production and recycling of wastes, the Earth could heal from the birth-pains of the human Industrial Revolution. As space elevators rose at the equator, and mining and heavy industry moved offworld, the Earth would once again become a garden, to be enjoyed by its human masters and lived in by many other species.
(*) Currently not structurally possible, but advances in the materials science of even the next 50 years, let alone the next 100-200, should make this relatively easy.
(**) This of course implies much vaster amounts of wealth per person, but unless something happens to check economic growth soon, that is exactly what's likely.