As explained here the delegates to the PA Democratic primary are apportioned by districts with the number of delegates allotted depending on the number of registered Democrats in the district (at the time of apportionment, unfortunately not including the many newly registered voters).
This means that the number of delegates per district varies considerably, ranging from 9 for district 2 (Philadelphia west) and to a mere 3 for the district 9 ("Altoona").
Because the geographic size of a district has nothing to do with its number of delegates an ordinary map can be deceptive. We are all familiar with the vast expanse of red states in the middle of the US whose collective voice hardly totals that of California and New York alone. For this reason I thought it would be useful to see a map with each district's size scaled to its number of delegates.
So here we have it.
The technical name for a map of this type is a cartogram. The simplest type of cartogram (shown here) is a "rectangular volume area" cartogram where little attempt is made to preserve the actual shapes of the districts. Since the data is fairly discrete (between 3-9 delegates per district) I've chosen simply to show each district with a certain number of squares where each square is one delegate. For example district 9 ("Altoona") is the size of three squares, so it has 3 delegates.
If two districts share a border geographically, they touch on this cartogram (it is a "contiguous" map). The positions of the districts are roughly correct geographically except for the position of Pittsburgh in the upper left corner.
Using special software, fancy cartograms can be produced that look prettier than this one, so if anyone knows how to make one I would be pleased to see it.
It's clear that much of the delegate count is concentrated in the southeast portion of the state. Philadelphia and adjacent districts, plus districts 8, 15, 16, 17, 19 (essentially Bucks Co. to the north, and the districts containing York, Lancaster, Harrisburg and Allentown) comprise about 60% of the delegates but cover less than 25% of the actual area of the state.
There has been some discussion of where Obama will be campaigning in PA during the upcoming bus tour. This map may help to clarify what is at stake where.