Richard Patterson for The New York Times

Richard Patterson for The New York Times

In the New River community the houses resemble those of suburbs from the past, except they are larger and closer together. Developers have done surveys to determine what potential owners want.

The Breuer family, standing from left, Monica, Andrew and Yolanda, and J. J., seated, with their dogs at their home in New River. A move from Tampa meant improvements like more square footage and a larger master bedroom.

WESLEY CHAPEL, Fla. - New River Township is, for the moment, the edge of beyond.

Its square mile of tightly packed homes is the outer crest of Tampa's residential swell, four miles from the nearest grocery store and 30 minutes from the nearest major mall. Just down the road, beyond some orange groves, cattle graze languorously amid the insect hum of a sun-baked field, and only a few mobile home parks and a roadside stand selling tiki huts interrupt the vast sea of pine, palmetto and dense thatch.

But it will be a short-lived isolation. More than three dozen other communities in Pasco County, some bigger than New River, are in the works, promising 100,000 new homes in the next five years. A megamall is coming. And the first of the big-box stores, a Home Depot and a Sam's Club, had their gala openings not long ago.

"It used to be just us and the retirees," said Ruth Parker, who was busy decorating a new child care center at the edge of New River, a part of Wesley Chapel, where she has lived for nine years. "Five years from now, there will be a city here."

America is growing. And it is growing the fastest here, at the farm-road margins of metropolitan areas, with planned communities sprouting up and becoming a prime focus, almost a fetish, for election strategists from both major parties.

Such places do not sprout by happenstance. Driven by irresistible economic forces and shaped by subtly shifting social patterns, they are being created, down to the tiniest detail, by a handful of major developers with a master plan for the new America. In the case of New River, that developer is KB Home, one of the nation's biggest and most profitable builders with $7 billion in sales last year, which helped make it sixth among all Standard & Poor's 500 companies in total revenues.

KB Home has 483 communities under development in 13 states and expects to complete more than 40,000 new homes this year. Yet it is just one of about two dozen such corporate giants fiercely competing for land and customers at the edge of America's suburban expanse.

Poring over elaborate market research, these corporations divine what young families want, addressing things like carpet texture and kitchen placement and determining how many streetlights and cul-de-sacs will evoke a soothing sense of safety.

They know almost to the dollar how much buyers are willing to pay to exchange a longer commute for more space, a sense of higher status and the feeling of security.

"You bring people out here, and they say, man, look at all this open space," said Marshall Gray, president of KB's Tampa division. "But I assure you, there are deals in the works for virtually every significant piece of ground you can see out here."

Over the next decade, New River will expand to 1,800 acres and be home to 15,000 people living in 4,800 single-family homes, condominiums, town houses and rental units. It will have a 200-acre town center with 180,000 square feet of office space, 500,000 square feet of commercial space, schools, government offices and a 207-acre park.

At the moment, though, it is nothing more than an island of 400 suburban homes in the middle of nowhere, an infant exurb.

The term "exurb" was coined in the 1950's in "The Exurbanites" by A. C. Spectorsky, a social historian, to describe semirural areas far outside cities where wealthy people had country estates. The exurbs of the 21st century are a different animal. And they are not the same as the older rings of closer suburbs.

The homes in exurbs are generally larger and the space between them smaller. They tend to turn their backs to the street, with the biggest and most used rooms in the rear. And the people who live in them are different. Instead of the all-white enclaves of the 1960's and 70's, the new exurbs are a mélange of colors and cultures.

A Different Kind of Flight

"In one sense, these exurbs are just suburbs that take a longer time to drive to," said John Husing, a political and economic consultant in California. "With these, white flight has nothing to do with it. It's all housing prices. The makeup of these communities is a reflection of who's migrating, and that's people who have enough money to be middle class."

Look deep into the history of many of the new exurbs, and an entrepreneurial character like Beat (pronounced BAY-at) Kahli, an Orlando-based developer, can often be found.