The U.S. Constitution Equal Protection Clause’s “one-person one-vote” principle requires that voting districts have roughly the same population so that votes in each district count equally. But what population is relevant—total population or total voting population—and who gets to decide? The Supreme Court will decide these issues in Evenwel v. Abbott. 

While this case involves a state legislature redistricting it is equally applicable to a local government drawing boundaries for a local election. While local governments may prefer to decide for themselves (rather than have the Supreme Court tell them) what population metric is appropriate, they may disagree about the better metric.

Texas reapportioned its state senate districts following the 2010 census based on total population alone. All parties agree the redistricting plan’s deviation from the ideal (8%) using total population is acceptable. But plaintiffs claim that depending on which voter-based metric (citizens of voting age, registered voters, etc.) is used, Texas’s plan “deviates from the ‘ideal’ district by roughly 46% to 55%.” Plaintiffs claim that their votes are worth less than other voters because they live in districts that substantially deviate from the “ideal” in terms of number of voters or potential voters, which violates the “one-person one-vote” principle.

The district court ruled in favor of Texas reasoning that the Supreme Court has never held any particular metric to be unconstitutional. Rather, the Court has stated that a population measure is viable as long as it is not the result of a discriminatory choice by the state legislature (which was not alleged in this case).

This grant comes as a surprise. Over the last 25 years the Supreme Court has denied certiorari in at least three other petitions (all involving local governments) arguing that voter population must be equalized in districts. Election law professor Richard Hasen wrote on his blog, "Like Texas, I had considered the issue fairly settled by the Supreme Court that states have the power to decide whether to use total population or another measure for drawing district lines."