I know anyone who's messed around with DRA a lot knows that there are certain patterns in gerrymanders that can be seen across different maps. The other day I was wondering if it were possible to codify the different types of districts that you see in Democratic and Republican maps. What I discovered is that it is much easier to codify the decision making options available to partisan mapmakers than it is to codify the different types of districts it results in due to varying demographics between states. While I may at some point later attempt a diary that semi-comprehensively lists the different types of districts, below the fold is my best attempt at distilling the theoretical decision making process of partisan mapmaking. Any feedback is welcome. Sorry if it's a bit too theoretical.
While the districts may look different because of differing geography and demographics, partisan map makers basically have a dualistic choice to make when dealing with territory that is strong for their party, territory that is strong for their opponent's party, and territory that is swingy.
The options for dealing with the opposing party's areas of strength are:
Swamping it by putting it in with enough territory that favors their own party that the overall district will support their candidates.
OR
Packing it into one district that will go as strongly for the opposing party as possible so that the territory can be kept out of districts the mapmaker wants for their own party.
Swamping is always preferably to packing from a partisan perspective where it is possible to do without weakening the party's own districts too much because packing concedes a district to the opposition.
The options for deal with your party's areas of strength are:
Diluting it by connecting it to swingy areas or areas that favor the other party.
OR
Compacting it by attempting to maximize their own party's strength in the district.
The decision to dilute or compact depends on the party's strength in the area and the strength the mapmakers want the districts to be. If the party is substantially stronger in the area than the mapmakers want the district to be, it makes sense to dilute the area. If the party's strength in the area is only barely where the mapmakers want it to be, or the opposing party has enough strength in surrounding areas to make diluting the area impossible or impractical, it makes more sense to compact the area.
The options for dealing with swing areas are:
Absorbing it by drawing it in with areas of strong support for their own party to create a districts that still favor their party but don't "waste" as many votes.
OR
Packing it into a district that will be swingy.
As with the opposing party's territory, absorbing is preferable to packing where possible, as a safe (or at least strong) district is preferable to a swing district. Partisan map makers should try to avoid putting swing territory into districts that favor the other party.
Finally, except when a district fits perfectly with a community of interest, there are two ways a map can treat a community of interest:
Splitting it between two or more districts that are connected to areas that are either swingy or favor the opposite political party as that community of interest. When splitting is done to swamp one of the opposing party's areas of strength, it is called cracking. There's no preexisting term for splitting to dilute the district down to the strength you think is necessary for your own party's district, but for the purposes of this diary I'll call it spreading. The extreme version of splitting is typically a baconmander.
OR
Combining it with other communities of interest that favor the same party. This can be done either to pack the opposing party's areas of strength into a vote sink or create a district that favors the mapmaker's party in otherwise hostile territory.
Many districts can be a hybrid of the two.
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