Two suggested implications: the poor have moved out to the suburbs, and central cities are undergoing a revitalization trend.
"Whereas inhabitants of Suffolk County, Massachusetts (which includes Boston) saw their median household incomes grow by 2% since 2000, people living in all three surrounding counties saw their median incomes decline. In New York, Manhattan saw local median incomes increase by 10% but suburbs counties Westchester, Bergen, Middlesex, and Union Counties all saw declines.
The City of Baltimore, Maryland kept household income relatively steady even as Baltimore County, which surrounds it, lost ground. Same story in the Washington, D.C. region, where the three center cities-Washington, Arlington, and Alexandria-each saw median incomes increase by about 10% even as near-in suburbs of Fairfax and Prince George's Counties, once known as two of the nation's most successful suburbs, saw a slight decrease.
Of course, these trends are not universal."