What makes a Community of Interest?

[muon2]

Most of the time CoI in redistricting refers to geographic units smaller than a county.  One problem with entirely tiling a state into multi-county CoIs is that population equality is going to force chops in some number of them. I did a regression analysis that shows the likely inequality based on the mean number of geographic units (like counties) per region (see item 6 in the muon rules thread.)

For regional CoI I recommend the work jimrtex did in putting together the Urban County Clusters (UCCs) based on collaborative threads here years ago, with the final version stickied on the board. The UCC avoids the population problems in mentioned above by recognizing that the CoIs tend to be stronger in metro areas, so it leaves the rural areas to float between districts to aid population equalization. The muon rules provide a means to reward plans that keep those UCCs as whole as possible without using them to dilute rural areas unnecessarily.

[muon2]

Most of the time CoI in redistricting refers to geographic units smaller than a county.  One problem with entirely tiling a state into multi-county CoIs is that population equality is going to force chops in some number of them. I did a regression analysis that shows the likely inequality based on the mean number of geographic units (like counties) per region (see item 6 in the muon rules thread.)

For regional CoI I recommend the work jimrtex did in putting together the Urban County Clusters (UCCs) based on collaborative threads here years ago, with the final version stickied on the board. The UCC avoids the population problems in mentioned above by recognizing that the CoIs tend to be stronger in metro areas, so it leaves the rural areas to float between districts to aid population equalization. The muon rules provide a means to reward plans that keep those UCCs as whole as possible without using them to dilute rural areas unnecessarily.

This kinda sounds like it'd work against Democrats more often than not though.   Urban areas would be bound together in a small number of districts and tightly pack Democratic voters, while rural areas could be slide in and out of districts to the benefit of Republicans.   

There should be some mechanism to keep the most sparsely populated areas of a state together in the same districts as there is to be keep densely populated areas of the state together, otherwise with the current political geography of the country the metrics would have a Republican favoring bias.

Our model state when we started was MI. The problem was that it was too easy to split the Dems in the 3-county Lansing metro under the guise of whole counties. We found that metro areas as defined by the Census were too big and grabbed a lot of unnecessary rural areas. That led to the specific metrics for selecting certain counties in a metro area for inclusion in the UCC. We tested the model with a variety of plans and found it kept the political balance reasonably well. We followed with plans for many states, and never found one where it did worse politically than metrics that ignored the UCCs.

Ideally metrics should not be shifted just because there is political realignment. That said, it's worth testing the metrics with new election data to see if there's an unanticipated bias. That requires plan makers to follow a set of metrics, an idea that seems to have fallen a bit out of favor compared to 10 years ago.

[muon2]

An expo-facto argument in favour of boundaries that favour my party.

I've seen that, for sure. In 2011 the IL Dems wrote a extensive resolution to accompany their new legislative plan. The communities of interest were written in detail and had little to do with the ones presented in 19 public hearings. However, their described CoIs exactly matched their plan and they admitted in floor debate over the map that it was drawn explicitly to favor their party.

[muon2]

'The primary factor should be if the voters of the district can easily identify what district they're in.  

I agree. That's the advantage of dividing the state into identifiable geographical subunits and then putting the subunits together to make districts. Larger districts like congressional work better if one starts with larger subunits. Smaller districts need smaller subunits to start. I've found that subunits that are no larger than 10% of the ideal district size work best.

This is from the analysis I did on whole county (and whole New England town) maps that were drawn for congressional districts on threads here last cycle. A range of 3.5 (average of 10 geographic units per district) is just under 0.5% of a CD. A range of 2.5 (average of 20 geographic units per district) is just under 0.05% of a CD.



The analysis would generally apply to any collection of subdivisions, not just counties. For example one could use school districts in populous suburban areas as better indicators of communities of interest that are easily identified by voters.

[muon2]

'The primary factor should be if the voters of the district can easily identify what district they're in.  

I agree. That's the advantage of dividing the state into identifiable geographical subunits and then putting the subunits together to make districts. Larger districts like congressional work better if one starts with larger subunits. Smaller districts need smaller subunits to start. I've found that subunits that are no larger than 10% of the ideal district size work best.

This is from the analysis I did on whole county (and whole New England town) maps that were drawn for congressional districts on threads here last cycle. A range of 3.5 (average of 10 geographic units per district) is just under 0.5% of a CD. A range of 2.5 (average of 20 geographic units per district) is just under 0.05% of a CD.



The analysis would generally apply to any collection of subdivisions, not just counties. For example one could use school districts in populous suburban areas as better indicators of communities of interest that are easily identified by voters.

I’m curious how counties play a role in states like Georgia, North Carolina, Texas, New York, and California when trying to run broad analysis like this. These states run the gambit of county size with some having counties that could have a dozen districts, or districts that could have a dozen counties.

I think a lot of this has to do the fact I come from a fuzzy area between major COIs so I’m especially interested as what to do with the buffer regions. I’d be interested to see a map of how you’d draw subsets in a given state so I could get a better idea of the concept if you happen to have a map handy

For the study used to make the graph I used plans that nested as many whole districts in a county as possible and attached the remainder to other counties. That's why the graph refers to regions, since some reflect multiple districts due to large counties. It doesn't imply that nesting districts is best, but nesting them made a uniform approach to handling large counties across the states.

There are lots of threads from 2012-2015 that looked at rational ways to subdivide large counties in different states. Most are available through the old 2010 redistricting directory thread. IIRC MI, WA, and VA got a lot of attention on big county subdivisions.

One important consideration we found based on the plans drawn and the observations of real legislative gerrymanders is that any geographic subdivisions have to be specified in advance and agreed to by all sides. It was too easy to construct gerrymanders (sometimes subtle) and then define the CoIs after the fact. Agreeing on subdivisions in advance block that sort of gerrymander.