Several macrotrends have broken Philadelphia's way: The city's population is growing again. Residential building is up, and the city has seen an influx of college-educated young adults over the last decade.

But one trend remains stubbornly negative, as three recent research reports make clear: The city continues to lose jobs. The latest such evidence was included in the Center City District's "State of Center City, 2013" report, released Monday.

The special-services district can rightly brag about the increased vibrancy in the area wedged between the rivers and Vine and Pine Streets. The city is cleaner since 1990, serious crime is down, and the churn in retail stores and restaurants is source of small-business strength.

Employment, though, remains a weakness, and if the long-term trend of job destruction does not change, it's hard to imagine that the city could continue to maintain momentum in other areas.

That prompted Center City District president and chief executive Paul R. Levy to set a goal for the city: adding 50,000 to 100,000 jobs by 2023.

"If you can turn around 50 years of population decline, you can turn around 50 years of employment decline," Levy said. "We need to set this goal."

Easy to say, hard to accomplish.

The Brookings Institution's Metropolitan Policy Program last week released its latest review of how "job sprawl" is affecting the urban cores of the 100 largest metro areas. In all but nine, the share of jobs within three miles of the core declined during the 2000s. Philadelphia experienced a 1.5 percent drop in employment.

In addition, with 15.2 percent of the region's 2.31 million jobs within 35 miles of Center City, Philadelphia, has among the lowest percentages of its employment in its urban core. That is well below the 22.9 percent average for those 100 metro areas.

Similarly, the Pew Philadelphia Research Initiative's fifth "State of the City" report, issued in late March, raised the question: "Can a city keep growing without an expansion of employment opportunities?"

Using Census Bureau data, the Center City District counts 279,412 of those jobs in the region it describes as Greater Center City - Center City itself, plus adjacent neighborhoods bounded to the north by Girard Avenue and the south by Tasker Street. Those jobs amount to 44 percent of all wage and salary jobs in Philadelphia.

That labor is going on largely in an office market whose inventory has not grown since 1990, however. Cira Centre and Comcast Center may have added 1.9 million square feet of space since 2005, but 30 other office buildings with almost 3 million square feet were converted to housing, Levy said.

Some large employers have migrated to other parts of the city, such as GlaxoSmithKline's recent move from 16th and Race Streets to the Navy Yard.

As he has for many years, Levy again called on city government to change its tax structure. He called Philadelphia's practice "taxing what moves," meaning wages and profits.

And unless the city rebalances how it taxes citizens and businesses, there will likely be little movement on reaching the goal of creating at least 50,000 jobs.

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