Our region's ego took a hit last month when the census estimated that the city of Pittsburgh is now only the 59th largest city in the United States, down from 54th in 2000, and smaller than places such as Aurora, Colo., and Bakersfield, Calif.

In 1950, Pittsburgh was the 10th largest city in the country, but its population has dropped by more than 50 percent since then, one of the largest population declines among any major city.

What caused this precipitous drop? High taxes? The loss of the steel industry? Bad city management?

The primary explanation is actually quite simple: With only 55.6 square miles, Pittsburgh is one of the tiniest of the major cities in the nation.

Among central cities in the top 40 regions, only Boston; Miami; Minneapolis; Providence, R.I.; and San Francisco are smaller in land area than Pittsburgh. Most big cities have at least twice the land area that Pittsburgh does.

In cities with more land area, many people who moved "to the suburbs" stayed within the corporate limits of the central city. But in Pittsburgh, the suburbs are different municipalities, and suburbanization meant population loss for the city.

However, while residents moved out, their jobs did not. Although Pittsburgh ranks only 59th in the number of residents, it ranks 25th in the number of jobs located in the city (in businesses of all types). In 2004, there were nearly 300,000 jobs in the city of Pittsburgh, more than in many cities that are much bigger in terms of population.

And the city would probably rank even higher if it weren't so small; Pittsburgh ranks sixth in the country in jobs per square mile, behind only Boston, Miami, New York, San Francisco and Washington, D.C.

The jobs located in the city of Pittsburgh support families throughout the entire region. In fact, only about a third are filled by people who live in the city. Nearly 200,000 people, from every county in southwestern Pennsylvania and from West Virginia and Ohio, come to Pittsburgh every day to work.

Most people don't realize how much our region's economy depends on the city of Pittsburgh. More than one of every four jobs in the Pittsburgh metro area is located in the city. Moreover, the city houses three-quarters of the region's higher education jobs, half of the jobs in finance and company headquarters, and more than one-third of the jobs in professional services, health care and arts and entertainment. Several of these are the sectors that have created almost all of the region's job growth in the past several years.

And of course, the city doesn't offer just jobs; it also is the region's primary source for advanced health care, higher education, culture, entertainment and sports, which are major attractions for talented workers, regardless of where in the region they live.

The challenge for the city is providing the public services needed to support these jobs and regional attractions, but with a tax base that depends primarily on a shrinking base of residents. Raising tax rates on either businesses or residents won't work, because it's too easy for either group to move across the city line to escape them. So it's critical for the city to attract more residents in order to increase its tax base.

Aren't the city's high tax rates a major deterrent to living in the city? Yes, but high gasoline prices are an equally high deterrent to living in the suburbs. What most commuters save in taxes by living in the suburbs is now more than offset by the cost of gasoline and depreciation on their car.

Because of the central role Pittsburgh plays in the region's economy, it's a priority for the entire region to make sure the city can attract and retain residents. Strengthening the city's finances and improving the quality of the city schools are particularly important.

Our region's future depends on having a healthy central city.