The five major cities in the United States with the largest percentage increase in their daytime populations, according to the U.S. Census Bureau:

Washington D.C. -- The nation's capital sees a daytime population jump of 72 percent. The District of Columbia has 572,000 residents crammed into just 61 square miles, which is only a slightly larger area than Pittsburgh. But as a national and international government center, buttressed by lobbying groups and think tanks, it pulls in a net influx of 411,000 commuters each day.

In recent years, District of Columbia officials have tried unsuccessfully to implement a commuter tax to help pay for municipal services, but the courts have upheld Congress's ban on such a tax. William Hudnut III, a former Indianapolis mayor and now an urban consultant who works in Washington, thinks that's wrong. Suburban commuters, he said, "come into town and they benefit from fire and police services and garbage pickup and snow removal services and they should help pay for that."

Atlanta -- The region's population soared almost 40 percent in the last census, but the city itself grew by only 6 percent, giving it an even smaller share of the region's population than Pittsburgh has. With such major employers as BellSouth, Coca Cola and Turner Broadcasting, however, the city pulls in 260,000 commuters for work. Atlanta also annexed its airport, allowing it to count those jobs as part of its total.

Bart Lewis, chief of the research division of the Atlanta Regional Commission, said the city has been unable to annex new land for 50 years, and "the reason is a nice, simple four-letter word: race. The city was viewed as where black people lived and it wasn't allowed to annex any more." On the other hand, Mr. Lewis said, in the years since then, the Atlanta region has done a better job of creating opportunity for African Americans than any other city in the South, and that has contributed to the city's vigorous job market.

Tampa -- With St. Petersburg and Clearwater occupying the peninsula west of Tampa, this Florida city is packed into its own spit of land jutting into Tampa Bay. But because it always has operated the port facilities in the region -- including a major stopover for large cruise ships -- Tampa remains the premier job center, pulling in slightly more non-residents each day for work than Pittsburgh does, and boosting its daytime population by 48 percent.

The city of Tampa is facing two challenges now, said Mickey Jacob, an architect on the board of the Tampa Downtown Partnership. One is a weak mass transit system. The other is a need to pull in more downtown residents, particularly young people working in biomedical and other creative industries. One catalyst for that growth, he said, will be the burgeoning University of South Florida, which recently surpassed Florida State University to become the state's second largest college.

Pittsburgh -- With its dubious reputation of having the most governments per capita of any county in the nation, Allegheny County's 129 suburban municipalities long have ringed the compact city of Pittsburgh. In the region's industrial heyday, much of the county's employment was spread out in steel towns along the rivers, while today, the city itself has become more of a job magnet for the region, pulling in a net influx of 138,000 working commuters each day.

Still, because those workers live elsewhere, the city isn't able to capture most of their local tax payments, said urban policy consultant David Rusk, and that helps explain why the city government is in such dire financial condition. Mr. Rusk said his studies have shown that cities that are able to expand their boundaries and encompass more of their affluent workers generally have much healthier municipal bond ratings.

Boston -- Amazingly, the historic city of Boston occupies even less space than Pittsburgh (48 vs. 56 square miles). But with its booming office towers and government centers -- it's also the state capital -- the city pulls in 242,000 net commuters each day. Because the Boston region is so densely populated, it often is easier for workers to take transit routes into the city to work than to drive from one suburb to another.

"My take on why Boston has maintained a high share of [the region's] jobs is because we have the agglomerating force of the major universities, which generate the impetus for biotechnology and other knowledge firms to come to the city," said Christopher Zegras, an urban planning professor at MIT.

In addition, he said, the Boston region put early limits on its highway building to try to meet clean air standards, and that has decreased some of the sprawl that has affected other large metropolitan areas.