Title:      Tobler�s Law, Urbanization, and Electoral
Bias: Why Compact, Contiguous Districts are Bad for the
Democrats

Authors:    Jowei Chen, Jonathan Rodden

Entrydate:  2009-11-11 15:29:55

Keywords:   elections, voting, party competition, legislative
districting, simulations, electoral geography, spatial
autocorrelation 

Abstract:   When one of the major parties in the United States
wins a substantially larger share of the seats than its vote
share would seem to warrant, the conventional explanation lies
in manipulation of maps by the party that controls the
redistricting process. Yet this paper uses a unique data set
from Florida to demonstrate a common mechanism through which
substantial partisan bias can emerge purely from residential
patterns. When partisan preferences are spatially dependent and
partisanship is highly correlated with population density, any
districting scheme that generates relatively compact, contiguous
districts will tend to produce bias against the urban party. In
order to demonstrate this empirically, we apply automated
districting algorithms driven solely by compactness and
contiguity parameters, building winner-take-all districts out of
the precinct-level results of the tied Florida presidential
election of 2000. The simulation results demonstrate that with
50 percent of the votes statewide, the Republicans can expect to
win around 59 percent of the seats without any "intentional"
gerrymandering. This occurs because urban districts tend to be
homogeneous and Democratic while suburban and rural districts
tend to be moderately Republican. Thus in Florida and other
states where Democrats are highly concentrated in cities, the
seemingly apolitical practice of requiring compact, contiguous
districts will produce systematic pro-Republican electoral bias.

http://polmeth.wustl.edu/retrieve.php?id=942

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