Why do Supreme Court opinions denounce some districts as political gerrymanders but say nothing about other superficially similar districts? Why does the Court deem some majority-minority districts unnecessary under the Voting Rights Act, or even unconstitutional, but uphold other apparently analogous districts? This Article introduces a concept — “spatial diversity” — that helps explain these and many other election law oddities. Spatial diversity refers to the variation of a given factor over geographic space. For example, a district with a normal income distribution is spatially diverse, with respect to earnings, if most rich people live in one area and most poor people live in another. But the district is spatially homogeneous if both rich and poor people are evenly dispersed throughout its territory.
Spatial diversity matters, at least in the electoral realm, because it is linked to a number of democratic pathologies. Both in theory and empirically, voters are less engaged in the political process, and elected officials provide inferior representation, in districts that vary geographically along dimensions such as wealth and race. Spatial diversity also seems to animate much of the Court’s redistricting case law. It is primarily spatially diverse districts that have been condemned (in individual opinions) as political gerrymanders. Similarly, it is the spatial heterogeneity of the relevant minority population that typically explains why certain majority-minority districts are upheld by the Court while others are struck down.
After exploring the theoretical and doctrinal sides of spatial diversity, the Article aims to quantify (and to map) the concept. Using newly available American Community Survey data as well as a statistical technique known as factor analysis, the Article provides spatial diversity scores for all current congressional districts. These scores are then used: (1) to identify egregious political gerrymanders; (2) to predict which majority-minority districts might be vulnerable to statutory or constitutional attack; (3) to evaluate the Court’s recent claims about various districts and statewide plans; and (4) to confirm that spatial diversity in fact impairs participation and representation. That spatial diversity can be measured, mapped, and applied in this manner underscores the concept’s utility.