Stephen Von Worley looked at 2010 Census data and compared it to the 2000 Census. Here is Philadelphia. Red indicates blocks whose population went down (solid red is complete depopulation), blue indicates blocks whose population increased (solid red indicates a doubling in population), and white indicates areas that did not have population in either census.
Check out other cities at Data Pointed. Philadelphia is unusual in that it does not show the general pattern of a red urban center surrounded by a ring of blue suburbs.