Think Pittsburgh lacks Harrisburg clout now?
This is just a straight line extrapolation of population changes from April 1, 2000 (the reference date for the 2000 decennial census) through July 1, 2009 (the latest Census Bureau estimates data) extended 9 months through to April 1, 2010 (the reference date of the 2010 decennial census, and thus the reference date for reapportionment/redistricting). This map is showing projected changes in the number of state house seats, which is impacted by the size of the county. So the colors should not be interpreted as a rate of population change in itself. Big counties may have a greater change in seats just because they are larger or smaller than other counties. Thus note the middle of the T showing up as neutral. That more reflects the low population densities out there, not that their populations are steady. Of course, the numbers are notional with respect to actual legislators since the maps will be drawn any way the powers that be want them to be.. but on average the map reflects the overall shift in representation.
No matter how you slice it you see the writing on the wall. West is down, and East is up.