Some people argue that instead of blaming gerrymandering for causing partisan gridlock, we should blame the tendency of Democrats to cluster in major cities, allowing Republicans to take control elsewhere in the state. But that assumes that gerrymandered districts reflect the geography of counties and municipalities, which is the opposite of what gerrymandering does.
Even if voters from the various parties are evenly distributed in an area, under the current system, politicians could easily gerrymander districts to reduce the impact of the opposing party.
Research we’ve seen suggests that while geographic clustering may play a small part in the outcome of PA elections, intentional gerrymandering plays a far larger part. The results of the 2018 election shows that maps matter: the congressional delegation, elected from a court-ordered map, much more closely reflects votes cast than in years past, while the difference between votes cast and seats won for PA House and Senate was even greater than in previous elections.