I think it depends on the state. Some states have laws that mandate counties & precincts remain undivided, as much as is practicable.
The effect of that, of course, is that it divides liberal urban centers and dilutes them into districts more likely to elect a conservative.
Naturally, I see that as a plus, while Democrats hate it. But it has another benefit. Instead of having a couple of congressmen who represent a city, suddenly there are many. If anything, this makes the cities have more effective representation in Congress.