Case Study 39.1: The Redistricting Model and the Missing Neighborhood

Background

Following the 2020 Census, a state legislature contracted with a redistricting analytics firm — Polaris Mapping — to develop proposed congressional district maps using census block-level population data. The state had five congressional districts and a population of approximately 3.2 million. The minority population was primarily concentrated in two metropolitan areas: a majority-Black urban core in the state's largest city, and a large and growing Hispanic community in the suburban ring around the second-largest city.

The legislature's formal instructions to Polaris were standard: produce plans that (a) comply with the one-person-one-vote requirement (districts within 5% of equal population); (b) keep districts geographically contiguous; (c) minimize county splits; and (d) maintain current majority-minority districts as required under the Voting Rights Act (the state had one existing majority-Black district).

The Data Problem

The redistricting analyst at Polaris, a 31-year-old political geographer named Fatima, ran her first analysis using the standard 2020 Census data and immediately noticed something unexpected. The Hispanic community in the suburban ring — which had been growing rapidly, according to American Community Survey estimates and local school enrollment data — appeared substantially smaller in the Census data than in any of the auxiliary data sources Fatima had checked. The Census recorded the Hispanic population in four specific suburban census tracts at levels roughly 18-22% lower than the ACS five-year estimates would have suggested.

Fatima investigated. The four tracts in question shared characteristics consistent with hard-to-count populations: high proportions of renter-occupied housing, high residential mobility, significant recent immigration, and several trailer parks and informal housing developments that may not have been fully captured in the Master Address File. The 2020 Post-Enumeration Survey's block group-level estimates — not publicly available for all areas, but accessible to Fatima through a research collaboration — were consistent with her concern: these tracts may have been undercounted by 15-25%.

The Redistricting Consequence

If the Hispanic community in these tracts is undercounted at 15-25%, the redistricting plan based on the official counts will draw district lines around a population that is systematically smaller than reality. Specifically:

Scenario A (using official Census counts): The Hispanic population in the suburban ring is concentrated enough to constitute approximately 38% of a proposed second district, below the threshold where it would be considered a majority-minority district under standard Voting Rights Act analysis.

Scenario B (using Fatima's corrected estimates): The actual Hispanic population in the suburban ring is likely concentrated enough to constitute 44-47% of that proposed second district — still not a majority, but approaching a "coalition district" threshold and changing the legal analysis under the VRA.

The Pressure

The legislature's Republican majority has expressed a clear preference for a map that keeps the existing majority-Black district (federal law requires it) but does not create any additional majority-minority districts. The existing majority-Black district, in their preferred map, is drawn generously — providing Republican majorities in the other four districts.

The Democratic minority in the legislature has hired its own analysts and is arguing that the Hispanic undercount in the suburban ring is significant enough to warrant a second VRA-analysis district.

Polaris has been hired by the full legislature (bipartisan contract), but Fatima reports to a senior partner who has made clear that the firm values its repeat business with the Republican-majority legislature.

Fatima's Dilemma

Fatima has several options:

Option 1: Report the official Census counts as the basis for her maps, as the contract specifies, without flagging the potential undercount. The contract language does not require her to investigate or correct for undercount.

Option 2: Include a technical appendix to her report documenting the potential undercount in the four tracts and its implications for the district population analysis, presenting it as a methodological caveat without recommending a specific map modification.

Option 3: Recommend that the legislature formally request block-level Post-Enumeration Survey data from the Census Bureau for the affected tracts and delay the final map until that data is available.

Option 4: Present two alternative maps — one based on official counts, one based on her corrected estimates — and explicitly note that the legal analysis under the VRA differs between them.

Discussion Questions

1. What are the specific Census undercount mechanisms (as described in Chapter 39) that are likely operating in the four tracts Fatima has flagged? How do the characteristics of these tracts — renter-occupied housing, residential mobility, informal housing developments — connect to the undercount mechanisms discussed in the chapter?

2. Evaluate each of Fatima's four options using the data justice framework: whose data and consent; who benefits; how are accuracy limitations being handled?

3. What are Fatima's professional obligations here? She has a contract with the legislature that specifies the use of official Census data. She has also identified a significant accuracy concern with potential VRA implications. How do these obligations interact?

4. The VRA prohibits district maps that have the effect of diluting minority voting strength. If Fatima's corrected estimates are accurate and the official-count-based map results in a district that does not reflect the actual minority population, does the legislature face VRA liability? Does Polaris? Does Fatima individually?

5. The partner above Fatima has made clear that Polaris values its relationship with the Republican-majority legislature. How should Fatima navigate this organizational pressure? What would a data justice framework recommend?

6. Suppose Fatima chooses Option 2 (technical appendix documenting the concern). The legislature's Republican leadership reads the appendix, notes that it is framed as a "caveat" rather than a recommendation, and proceeds with the official-count-based map. Has Fatima fulfilled her professional obligation? Has she fulfilled her data justice obligation? Are these the same thing?

7. Democratic minority legislators subsequently cite Fatima's technical appendix in a VRA lawsuit. The appendix is used as evidence that Polaris knew about the undercount concern and proceeded anyway. Does this change your evaluation of Option 2 as Fatima's choice?