In the news today there are stories about how both the plaintiffs and defendants in the lawsuit over congressional district maps are claiming that the other side ‘must have’ drawn the maps intentionally to favor one party or another. What’s missing from the conversation is the basic fact that the geographic distribution of votes matters a lot in our system.
I conducted an analysis of the implication of this distribution and found some interesting results:
1. Under our current single-member district system, there is a natural advantage to a dominant party.
2. In a state with few seats, that advantage is magnified because the districts cannot easily be divided.
3. It is easily shown that achieving proportional outcomes and increased competitive districts would actually require maps to be drawn to purposefully benefit the non-dominant party or there would have to be highly unusual geographic luck.
4. The default expectation in a state like Utah where the maps are drawn to satisfy neutral requirements is a 4-0 outcome. Moving away from that outcome to get a 3-1 outcome requires very specific geographical distribution or intentionally drawn maps.
5. Detecting whether a map that yields a 4-0 outcome was intentionally drawn to favor the dominant party is virtually impossible based on the predicted outcomes, as many disproportionate results can be plausibly attributed to the natural distribution of voters.
Here is the full analysis.
Executive Summary: Analysis of Geographic Distribution on Congressional Elections
This report analyzes how the natural geographic distribution of voters, combined with the single-member district system, creates outcomes that structurally favor the dominant party, often leading to disproportionate representation and non-competitive districts, even without intentional partisan manipulation.
Initial Assumptions and Scope
The analysis is built on a simple, hypothetical model state to isolate the effect of geography:
- Partisan Split: A fixed 70% support for the dominant Purple party (P) and 30% support for the minority Pink party (K).
- State Size Models: The analysis is conducted using two scenarios:
- A 10-seat state to demonstrate basic principles.
- A 4-seat state to show how the structural effect of indivisible seats is magnified.
Key Findings
- Structural Advantage is the Default: The U.S. system of single-member geographic districts inherently rejects proportional representation, prioritizing local accountability. This structure naturally amplifies the majority party’s statewide advantage.
- Geographic Models Dictate Outcomes:
- Uniform Distribution (Natural Cracking): If the 70%-30% split is perfectly even across the state, the dominant party (Purple) will win 100% of the seats (e.g., 10 Purple – 0 Pink in the 10-seat model), as the minority vote is cracked (diluted) across every district.
- Concentrated Distribution (Natural Packing): Achieving the proportional result (7 Purple – 3 Pink) requires the minority party (Pink) to be naturally packed into dense geographic areas. This results in non-competitive districts (blowout wins) for both sides.
- Fragility of Proportionality: The report demonstrates that any intermediate or mixed geographic distribution will likely result in a highly disproportionate outcome (9 Purple – 1 Pink or 10 Purple – 0 Pink). In the 4-seat state, the proportional 3 Purple – 1 Pink result is fragile and easily tips to a 4 Purple – 0 Pink clean sweep for the majority.
- Conclusion: The analysis suggests that structural disproportionality and non-competitive districts are the default conditions of the single-member district system when one party holds a significant statewide advantage. Achieving proportionality often requires map drawers to intentionally pack the minority party’s voters to overcome this natural, structural bias.
Scholarly Context and Limitations
The analysis concludes by addressing the difficulty of applying these findings to the real world:
- Intertwined Effects: Both natural geography and intentional manipulation produce the same effect—disproportionate seat results—making it nearly impossible to distinguish cause from the final map outcomes alone.
- Metric Challenges: Quantitative measures of partisan bias (like the Efficiency Gap) often perform poorly in the specific circumstances analyzed (highly dominant parties or states with few seats), as they fail to reliably separate a naturally disproportionate outcome from a deliberately rigged one.
- The Burden of Proof: Since the system already grants a substantial structural advantage to the dominant party, the only way to confirm partisan gerrymandering is often by obtaining clear evidence of intent (e.g., internal communications), as many disproportionate results can be plausibly attributed to the natural distribution of voters.
