Here is the new map of the 21st State House Distinct. The green parts are the old district and the aqua blue line is the outline of the new district.
The 21st District had to add some population to it and also was facing other city Representatives that had to expand out because of population loss. Overall this district looks pretty good for the incumbent, Rep. Dom Costa. It adds more of Ross Township to the 21st, but Rep. Costa's base is in Bloomfield, Morningside, and the North river towns of Millvale, Etna, and Sharpsburg. Also added to the Democratic city base is part of Lawrenceville.
This should be a very solid Democratic seat and the only real election would be in the spring primary. From what I hear Dom Costa is popular with every faction of the city Democratic Party. If anyone decides to run against him and make it a race, it would have to be someone from Ross Township. It would be an uphill battle because he has represented most of Ross Township since 2008.
I also should mention that the State House GOP tried to force Dom Costa and Adam Ravenstahl to face each other by putting them both in the 21st District (h/t Early Returns). However, the backlash of the greedy power grab that created 2 Allegheny County seats with no incumbents living in them must have forced House Republican leadership to split the district between Costa and Ravenstahl.
Incumbent: Dom Costa (Democrat)
Possible Challengers: Matt Drozd (h/t politicspa)
Another tough seat in a Presidential year for a Republican, especially one that not a moderate in any way.