Jonathan Rodden and Jowei Chen argue that Democrats are underrepresented in Congress and state legislatures because they tend to live in high-density areas. Geographically-compact districting plans will tend to pack Democratic voters into districts where they have 80% of the vote or whatever, thus wasting their votes. They do a voter- and precinct-level analysis of recent elections and find:
In contemporary Florida, partisans are arranged in geographic space in such a way that virtually any districting scheme favoring contiguity and compactness will generate substantial electoral bias in favor of the Republican Party. This result is driven largely by the partisan asymmetry in voters' residential patterns: Since the realignment of the party system, Democrats have tended to live in dense, homogeneous neighborhoods that aggregate into landslide Democratic districts, while Republicans live in more sparsely populated neighborhoods that aggregate into geographically larger and more politically heterogeneous districts. This phenomenon appears to substantially explain the pro-Republican bias observed in Florida's recent legislative elections.
I have just a few things to add to their analysis:
1. More fundamentally, I guess this might be considered a pro-rural or pro-suburban bias, or an anti-urban bias which would fundamentally alter the representation of different parts of the state, no matter which parties happen to represent them.
2. If more Democrats tend to win in super-safe districts where they get 70% or 80% of the vote, does this imply that they will be more free in their voting patterns to indulge their personal preferences, compared to Republicans who (on average) might be under more electoral pressure and have to worry more about reelection?
3. Maybe multimember districts would be a way to balance the playing field. Is this a proposal that Democrats in Florida (or elsewhere) should be making?
Further discussion here.