Congressional Districts - 2016 ACS estimates.

[muon2]

With 5 of 18 IL CDs on jimrtex's list of the undersized, it's pretty clear why IL must lose at least one CD. The 5 include two minority CDs from Chicago, two CDs from outside Chicagoland, and 1 that skirts the exurbs into downstate. Three are solid D and two are R, but the R seats are at opposite ends of the state. If the loss is only one CD, as currently forecast, I can imagine wholesale changes as the Dems try to maintain the same representation for Chicago and force the loss on the Pubs.

[muon2]

With 5 of 18 IL CDs on jimrtex's list of the undersized, it's pretty clear why IL must lose at least one CD. The 5 include two minority CDs from Chicago, two CDs from outside Chicagoland, and 1 that skirts the exurbs into downstate. Three are solid D and two are R, but the R seats are at opposite ends of the state. If the loss is only one CD, as currently forecast, I can imagine wholesale changes as the Dems try to maintain the same representation for Chicago and force the loss on the Pubs.

If Dems have full control over redistricting, which requires Rauner to go or Madigan to gain a greater legislative control, I have always assumed the loss would be 12/13. With the 12th shrinking, it perfect sense for the Dems to cut one, and then combine the most Democratic bits to try to create another democratic seat. Some bits might be needed for 17th, but with Chicagoland marching leftward, it might just be easier to go grab some of the suburbs.

The 17th is probably the biggest challenge for the Dems. They can either stick a finger into Springfield and Decatur like the 2001 map or run a finger down the river to E St Louis. Either way that takes a piece out of what they probably need to make a southern IL CD. The south has just been swinging so far R the last few cycles, that it becomes harder and harder to build a Dem district.

I do agree that they'd likely dismantle IL-16 and try to run fingers further out from Chicago in to the burbs. Keeping 3 black CDs will be their challenge in Chicago. The areas immediately south and west of the Loop in IL-7 have been gentrifying and losing black population. That population has been dispersing or leaving the state and that means it is hard to replace with the next tier of suburbs out from the city.

[muon2]

Is it possible that Illinois will only be required to have 2 BVAP majority districts? 

The question is more whether the Democratic legislature would draw a map going down from 3 to 2.

This is correct. IL probably wouldn't have been required to have 3 black VRA CDs in the current map if a 2-CD version was drawn. Politically that wasn't going to happen. The same thing was seen in the last state legislative map, where even though there was a decrease in the black population in Chicago enough for 2 house districts, the map was drawn so that there would be no decrease in seats that would be likely to be won by the candidate of choice of the black community.

[muon2]

What district would be lost in Alabama?

Assume with Republican control you have to have:

1. VRA district in Birmingham, Selma, and Montgomery (AL-7)
2. Mobile-based district (AL-1)
3. Suburban Birmingham district (AL-6)
4. Huntsville-based district (AL-5)

1st district has to expand east into the 2nd district.
5th district has to expand south into the 4th district.

AL-3 and AL-4 have the most senior Republicans who also happen to be too young to retire. If driven by personalities and the same people are in office in 2020, I imagine Martha Roby loses her seat with some bits going to the 1st (rural south) and 7th (Montgomery) and the rest merging with the 3rd.

An alternative is to divide up the 4th with the 5th taking a big chunk, the 6th getting rid of rural counties south of Shelby and going west, and the 3rd taking up the populous east of the district.

This is what I posted in 2015 using whole counties except for Jefferson. I expect that a Pub gerry would add the city of Montgomery to the VRA CD and shift the other southern AL CDs to compensate. It chops up AL-3 between AL-2, 4 and 6. If there was an agreed retirement from one of the Pubs then that CD would get chopped instead.

[muon2]

The method jimrtex used starts with the existing CDs and moves toward a new, more balanced set using 2020 projections. This tends to weight the preexisting CDs as a criteria. I decided to take a blank slate approach that I though would be instructive for comparison.

I also used the 2016 Census estimates and projected them out to 2020 on a county level. Then I found the multicounty UCCs and used them as seeds for the 17 districts:

Philadelphia UCC: 5.494 CDs
Pittsburgh UCC: 3.005 CDs
Allentown UCC: 0.896 CD
Harrisburg UCC: 0.707 CD
Scranton UCC: 0.693 CD
Bloomsburg UCC: 0.112 CD

The Pittsburgh UCC uncloses Greene county so effectively I had to work with a UCC of 3.053 CDs. I split that UCC, taking a pack penalty, but created a region that could be split with only Allegheny county chopped. So don't be alarmed by the strange shape of the region, since the three eastern counties make up 2/3 of a CD and would get the rest from eastern Allegheny creating a reasonably shaped district.

There are only two CDs, Williamsport and Allentown, that are outside a 0.5% tolerance from the quota. Both are close enough to the quota that no macrochops are needed. Of course it's unlikely that these projections are accurate enough for a 0.5% tolerance, but I'm using them as if they are accurate for the exercise.



Philadelphia: 7.006 CDs
Allentown: 0.979 CD
Reading: 0.999 CD
Harrisburg: 0.998 CD
Scranton: 0.997 CD
Williamsport: 1.018 CD
Altoona: 1.003 CD
Pittsburgh: 3.002 CDs
Erie: 0.999 CD

Within the Philly region, Philadelphia+Montgomery+Bucks is 4.047 CDs and the rest is 2.959 CDs. Since the shift is less than 5% it would normally mean a macrochop would be avoided. However, both Philadelphia and Montgomery are more than one CD and have to be macrochopped anyway. The extra piece which would go with a CD to the west doesn't change that.

[muon2]

Your array of counties within the Philly zone does not comport with Jimrtex's map. Berks was excised, and 3 counties to the west added. That adds up to a cover and pack penalty no?

Berks is not in the UCC, so there would be no penalties for my Philly region. About half a CD has to come out of Chester, leaving a pack of 5 CDs in the rest of the UCC. Ideally Philly would get 2 CDs, Bucks would add a piece from Philly and Montco to form 1 CD, Montco would get 1 CD, and a sliver of Montco would combine with Delco and a third of Chester for 1 CD.

[muon2]

Why on earth have I thought all this time that Berks was in the UCC? 

Because there is a small yet significant exurban region in the south of the country - in don't know.

Reading forms a MSA separate from Philly and consists only of Berks. It has enough urbanized area population to be a single county UCC. Berks is part of the larger Philadelphia CSA.

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That's what makes Gill v Whitford so interesting. SCOTUS could for once set a standard to block political gerrymandering. If they do, it could be very narrow and affect WI and little else, or it could be expansive and apply a standard to all partisan redistricting plans. In the expansive case there will be a lot more emphasis on finding neutral standards to draw a map.

[muon2]

Has anyone in the Wisconsin case via an amicus brief or otherwise pointed out that the efficiency metric pushed by the Dems takes no cognizance of chops? In other words, any metric which focuses on chops and erosity (including - to deal with the Michigan law fail - intra-county erosity where a county is chopped), should not be characterized as an illicit gerrymander even if the result is "inefficient?"

I think that's going to be a point for SCOTUS to address. There are a number of issues with the efficiency test, and we had a whole thread on it earlier this year. Based on scotusblog, if the justices decide to rule that there is justicable partisan gerrymandering they may be prone to go for some version of Breyer's proposed test:

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It will come down to Kennedy and whether he thinks the time has come and technology has advanced to the point that the issue can no longer be avoided. I note that Breyer's test keeps to generalities and doesn't endorse a specific metric.

As for chops and erosity, the muon rules have five measures that are generally independent of each other, two of which are political - polarization and skew. The effect of a SCOTUS ruling here could be to cap the amount of skew, much like population inequality is effectively capped by SCOTUS.