Before the Supreme Court weighs in, let’s look at how other countries redistrict. How does redistricting differ in the United States from elsewhere? Are there lessons for Americans in these varying experiences and procedures?

According to the Supreme Court, the Constitution requires that population must be equalized across districts. The idea is that if one Arizonan lives in a district with 1 million other voters while another Arizonan lives in a district with only 200,000 other voters, the second one’s vote is more influential in choosing a member of Congress. Of course, populations shift, growing or shrinking over time.

To prevent those shifts from leaving unbalanced districts, state legislatures must redraw their electoral districts every 10 years, after the Census Bureau releases its new population data. Redistricting regularly leads to heated political and legal fights as legislators scramble to gain advantage for their parties.

Although the Supreme Court has ruled that the Constitution and the 1965 Voting Rights Act ban race-based gerrymandering — gerrymandering that reduces the power of one racial group’s votes — it has so far been unwilling to stop gerrymandering that twists districts to favor one party or another.

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Academic experts say the 2010 redistricting round was the most extreme in the nation’s history. That’s because of two factors: a stark partisan imbalance in control of state legislatures and governorships, and new computer technology that makes it possible to draw extremely fine-tuned partisan borders.

The power of state legislatures to engage in blatant partisan gerrymandering may change once the Supreme Court decides Gill, a case in which a federal district court in Wisconsin overturned that state’s congressional redistricting plan, deciding that a partisan gerrymander was banned on the ground of the Constitution’s equal protection clause and, critically, on grounds of First Amendment political speech rights.

What does redistricting look like elsewhere in the world?

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Redistricting looks quite different elsewhere, for several reasons.

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1. Larger districts send more than one representative to the legislature

Most democracies outside the English-speaking world elect more than one representative per district. When the number of seats per district can be adjusted, the principle of “one person, one vote” can often be achieved without redrawing boundary lines at all. You simply add a seat to a district that has grown, and subtract that seat from one that shrink. That vastly reduces the possibility of reshaping outcomes by manipulating boundaries.

2. Politically neutral bodies draw districts

In most other long-term democracies, a politically neutral body draws new districts — perhaps a quasi-judicial body or nonpartisan administrative board or commission. The redistricting bodies of some countries, such as New Zealand, include representatives of the major parties.

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But the more common pattern is to explicitly exclude anyone with partisan connections, as is true in Canada and India. In Britain, the ‘redistribution of parliamentary constituencies is carried out by a nonpartisan Boundary Commission. Parties can object to the commission’s redistricting recommendations, but it’s purely a consultation; their overall influence is limited. In some long-term democracies, such as Britain, legislatures must approve the new electoral maps that have been drawn by independent bodies, but this is typically a formality.

3. District boundaries are harder to manipulate

Unlike those in other countries, district boundaries in the United States are easy to manipulate. Lines are not required to respect preexisting political boundaries; districts are permitted to cut across such boundaries in a variety of ways and can end up resembling amoebas or starfish.

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Americans might be surprised to learn that the single-member districts in Mexico are drawn in concordance with an algorithm developed by a so-called technical committee implementing “good government” criteria of districting. The committee’s map is then submitted for two rounds of review by the political parties. Modifications are accepted only if they improve the value of a pre-established scoring function.

4. Legal challenges are more limited

The redistricting process runs through the courts astonishingly often. Few redistricting plans escape court challenges. Since Baker v. Carr (1962), federal and state courts have intervened in hundreds, perhaps thousands, of cases. Scores of these have made their way up for review by the Supreme Court. Most legal challenges are based on language from the Constitution — especially the equal protection clause of the 14th Amendment, or Article I.

In some established democracies, such as Japan, there have been important “one person, one vote” cases. The meaning of the proportionality principle has been litigated in countries such as Germany and Switzerland. In Britain, Canada and many Anglophone African countries, judicial review is permitted but rarely used.

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However, in most other countries, legal challenges are limited, and there is not the same concern for strict population equality. In some less democratic countries, such as Pakistan, the courts are actually prohibited from becoming involved in redistricting.

Some of that reflects differences in legal culture. But one key reason for the rarity of legal challenges in most countries is that they simply don’t face the kind of political manipulations and grossly distorted district lines endemic in the United States.

France is the long-term democracy whose process is most like that of United States. There, districts are drawn by the executive branch and reviewed by a constitutional council. But the process is handled at the national level, not by regions or states. Research by Nicolas Sauger of Sciences Po in Paris, in collaboration with one of the present authors, finds that the level of partisan bias in French parliamentary redistricting is minuscule.

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How could redistricting be changed to reduce gerrymandering?

Single-seat, winner-takes-all districts could be replaced by multi-seat districts with some form of proportional representation. Less drastic changes, such as California’s shift to a commission-based form of districting, could also be implemented. The change that’s most likely involves more direct court scrutiny of the most egregious partisan aspects of the redistricting process.

If the Supreme Court does not affirm the lower court decision in Gill v. Whitford and enunciate a manageable standard for declaring a plan to be an unconstitutional partisan gerrymander, we can count on rampant partisan gerrymandering in the 2020 redistricting cycle.

Bernard Grofman is the Jack W. Peltason Chair of Democracy Studies, professor of political science and adjunct professor of economics at the University of California at Irvine.

German Feierherd is a postdoctoral research associate at Yale University’s Program on Democracy.