Wisconsin Redistricting Plans

Data note

The original version of this memo included all the plans submitted to the Wisconsin Supreme Court in December 2021. On January 10th, 2022, the Court accepted corrected versions of the Assembly and Senate redistricting plans submitted by Governor Evers and BLOC. This memo has been updated to include these small corrections from Evers and BLOC. The changes were mostly designed to improve plan conformity with current municipal boundaries. Compared with the original submission, Evers’ corrections changed the Assembly district of 339 residents and the Senate district of 275. BLOC’s corrections change the Assembly district of 245 residents and the Senate district of 161.

On the same day, SCOWIS also rejected an alternative Congressional redistricting plan submitted by Wisconsin’s Republican Congressmen. Accordingly, I do not consider that plan in this memo.

Degree of Change

Since the legislature and governor failed to reach an agreement on redistricting, the process has moved to the Wisconsin Supreme Court. In December, the Court’s conservative majority decided to adopt a “least change” approach to the existing districts. Since these districts were created by a strong Republican gerrymander in 2011, any districts created by this process will be a victory for the GOP.

That said, some variation is still possible within the framework of “least change.” Six different entities submitted plans to the Court, which may choose one of them or draw their own. The planners are:

• Governor Evers
• the Republican-controlled legislature
• the Milwaukee-based advocacy group Black Leaders Organizing Communities (BLOC),
• State Senator Bewley (representing Senate Democrats)
• a Democratic-aligned activist named Lisa Hunter
• a group of intervenors going by the name Citizen Mathemeticians and Scientists (MathSci) who use computational redistricting techniques.

Neither Bewley nor BLOC submitted a Congressional redistricting plan. Incidentally, the Bewley plans for Assembly and Senate are the only maps submitted which use the wards recently drawn by local governments as their building blocks. All the other plans use 2020 census blocks.

Population preserved

The simplest measure of “least change” is just the share of the population moved from one district to another in a given redistricting plan. By this measure, Evers’ plan makes the fewest changes–moving just 14.2% of Wisconsin’s population into an Assembly district with a new district number.

The Legislature’s plan moves slightly more Wisconsinites into a new Assembly seat (15.8%). BLOC and Bewley move incrementally more, 15.9% and 16.4%, respectively.

The Hunter and MathSci plans appear to have given little effort to “least change” considerations. The Hunter plan moves 26.9% of the state into a new Assembly district, while the MathSci plan moves 39%.

Portion of population placed in the same district
in proposed redistricting plans
	assembly	senate	congress
evers	14.2%	7.8%	5.5%
legis	15.8%	7.8%	6.5%
bloc2	15.9%	10.4%
bewley	16.4%	9.5%
hunter	26.9%	19.2%	7.0%
mathsci	39.0%	25.7%	8.5%

District overlap

District numbers are not necessarily meaningful. A planner could closely preserve the boundaries of existing districts while also changing the numbering scheme entirely. But in practice, none of the planners did this in their final submissions.

For each submitted plan, I calculated the overlap between new an old districts. In the Legislature’s Assembly plan, 98 of the new districts primarily overlap with the old district using the same number. Ninety-seven of the districts in Evers’ and BLOC’s plans do so, as do 96 of Bewley’s, 90 of Hunter’s, and 80 of MathSci’s. Only the MathSci plan contains a senate district which doesn’t mainly overlap with the same old senate district. All the proposed new Congressional districts mainly overlap with the same old Congressional district number.

Number of districts mainly overlapping with the same old district
in proposed redistricting plans
	assembly	senate	congress
mathsci	80	32	8
hunter	90	33	8
bewley	96	33
bloc2	97	33
evers	97	33	8
legis	98	33	8

Population targets

While all plans draw Congressional districts with essentially identical populations, they do vary in how closely they attain the ideal population for Assembly and Senate districts.

In both cases, the MathSci maps come closest, followed by the legislature’s plan. Evers’ plan, although making the fewest changes to district boundaries, also comes less close to the ideal population for each district.

The preferred measure of a plan’s overall deviation from the ideal population is the range between the largest and smallest district, expressed as a percentage of the ideal district population.

The Legislative Reference Bureau offers a detailed discussion of “constitutional standards for equal population” in this memo. Strict population equality is the standard for congressional districts. The Supreme Court lets state legislative districts vary by as much as 10%. Standards seem to be tighter in Wisconsin. “In recent decades, Wisconsin’s state legislative redistricting plans have fallen well below that 10 percent threshold, achieving a maximum overall range of less than 2 percent going back at least to 1982.”

Population summary statistics for legislative districts
in proposed Wisconsin redistricting plans
	min	median	ideal	max	sd	range1	range as % of ideal2
congress
legis	736,714	736,715	736,715	736,715	0	1	0.00%
mathsci	736,714	736,715	736,715	736,715	0	1	0.00%
evers	736,714	736,715	736,715	736,716	1	2	0.00%
hunter	736,714	736,714	736,715	736,716	1	2	0.00%
assembly
mathsci	59,315	59,522	59,533	59,753	131	438	0.74%
legis	59,312	59,548	59,533	59,764	130	452	0.76%
bloc2	59,141	59,511	59,533	59,925	234	784	1.32%
hunter	58,980	59,501	59,533	60,063	242	1,083	1.82%
bewley	58,976	59,522	59,533	60,080	331	1,104	1.85%
evers	58,996	59,522	59,533	60,117	329	1,121	1.88%
senate
mathsci	178,131	178,572	178,598	179,026	277	895	0.50%
legis	178,092	178,550	178,598	179,118	216	1,026	0.57%
hunter	177,745	178,507	178,598	179,443	421	1,698	0.95%
bloc2	177,681	178,599	178,598	179,400	465	1,719	0.96%
evers	177,556	178,661	178,598	179,710	551	2,154	1.21%
bewley	177,010	178,567	178,598	179,879	821	2,869	1.61%
1 largest district population minus smallest district population
2 range as a percent of the ideal district size.

Change map

The map below shows precisely which areas of the state switch districts under each plan. The initial layer shows the existing districts drawn in 2011. Select a different radio button to view the lines under each proposed plan. For each plan, those areas of the state which change districts are shaded. District boundaries are slightly simplified for mapping purposes.