Our democracy depends on the belief by citizens that elections are free and fair, and that the resulting government bodies are legitimate. However, with rampant gerrymandering of district boundaries, it is widely recognized that elections are skewed toward those holding political power, thereby perpetuating their favored positions.

In its landmark decisions, Reynolds vs Sims (1964), Baker vs Carr (1962), Wesberry vs Sanders (1964), and Avery vs Midland County (1968), the U.S. Supreme Court held that districts with widely varying population numbers within a state are inherently unconstitutional, resulting in the equal population rule. Another widely recognized criterion, which has not been enforced, perhaps because of the lack of a clear metric for measurement, is that districts be compact.

Currently, many districts are custom designed to provide unfair partisan advantage. A straightforward way to make redistricting fairer is to enforce compactness along with the equal population rule. The requirement to maintain districts giving protected classes of voters such as black or Native American a chance to elect someone from their own group could be accommodated within this framework.

An elegant approach to determining if districts are compact is to require that in drawing district boundaries, the total length of those boundaries be minimized. This would result in relatively compact districts, in contrast to the sprawling distorted districts which are often created under the current systems. With computer technology such as GIS (geographic information systems), minimum boundary length and equal population can be implemented.

The U.S. Supreme Court listened to oral arguments this week on a reapportionment case from Wisconsin (Gill vs Whitford) in which the U.S. 7th Circuit Court of Appeals in Chicago ruled that the districts created by the state legislature are unconstitutional because they were impermissibly drawn to favor candidates from one party (Republican), thereby depriving voters from the other party (Democratic) of their right to choose their own representatives.

The lawyers for the plaintiffs argued that an acceptable criterion for judging the fairness of reapportionment is the difference between the percentage of votes cast for each party’s candidates and the percentage of seats won by each. In the 2012 Wisconsin election, Republicans won 48.6 percent of the total vote cast while obtaining 60.6 percent of the legislative seats. With less than half the total vote, Republicans in Wisconsin obtained a substantial majority in the legislature.

While this percentage difference is a valid measure of malapportionment, its use in evaluating districts is hard to implement because these percentages depend on how many people are registered to vote, how many actually voted, and how they voted. Thus, the measure is a moving target that would be different for each election, and could only be computed based on prior elections.

An important advantage of the minimum boundary length system is that it is independent of the number of citizens registered to vote, actually voting in prior elections, or how they voted.

In contrast to the use of prior election results in judging the fairness of district boundaries, basing the criteria on the total length of boundaries for all districts combined, along with equal populations, is conceptually unambiguous. The district boundaries created under this rule could be challenged only by presenting an alternative set of districts with more nearly equal populations and shorter boundaries. In densely populated areas such as metropolitan Chicago, the central city districts would be physically small. Sparsely populated rural districts would include a large territory.

Justice Anthony Kennedy has indicated openness to looking at the issue of compactness if there is a robust tool for judging. This proposal could provide the court with an appropriate tool.

When the equal population rule was implemented in state government, there was a huge shift in political power from entrenched rural interests from sparsely populated counties to heavily populated urban areas, resulting in dramatic improvements in governance. Implementation of a minimum boundary length rule has the potential to shift political influence from the far left and far right of our political spectrum toward the center, which would better represent the preferences of the U.S. population.

R. Bruce Billings is professor emeritus in the Department of Economics of the University of Arizona.