Young professionals and empty-nester baby boomers are flocking to urban areas and reshaping the downtowns of some of the largest U.S. cities.

Texas, in particular, is enjoying this trend. It's now home to three of the nation's 10 most populous cities: Houston , Dallas , and San Antonio . These cities are literally growing up — high-rises are filling old industrial sites and abandoned neighborhoods.

The trend also is accelerating in Phoenix , Las Vegas , and other cities that have never had real urban centers. Phoenix is building a light-rail system with high-rises being developed all along the rail line

While high-rises aren't new to Las Vegas , the new ones are getting bigger and taller. For example, on the Las Vegas Strip, MGM-Mirage's 76-acre Project CityCenter will be a mixed-use community containing multiple high-rise buildings with city offices, luxury condos, a hotel and casino, and a retail and entertainment district.

"It's a new culture for us in southern Arizona ," says Debra Allen "East Coast cities have had that higher-density flavor for some time. For us, it's a new experience."