Mathematicians are deploying algorithms to stop gerrymandering | MIT Technology Review
With the 2020 US Census data release, states start the process of redrawing district maps. New computational tools will help hold politicians to account.
Siobhan Roberts archive page
August 12, 2021
conceptual illustration of a map being cut up and taped together
The maps for US congressional and state legislative races often resemble electoral bestiaries, with bizarrely shaped districts emerging from wonky hybrids of counties, precincts, and census blocks.
It’s the drawing of these maps, more than anything—more than voter suppression laws, more than voter fraud—that determines how votes translate into who gets elected. “You can take the same set of votes, with different district maps, and get very different outcomes,” says Jonathan Mattingly, a mathematician at Duke University in the purple state of North Carolina. “The question is, if the choice of maps is so important to how we interpret these votes, which map should we choose, and how should we decide if someone has done a good job in choosing that map?”
Over recent months, Mattingly and like-minded mathematicians have been busy in anticipation of a data release expected today, August 12, from the US Census Bureau. Every decade, new census data launches the decennial redistricting cycle—state legislators (or sometimes appointed commissions) draw new maps, moving district lines to account for demographic shifts.
In preparation, mathematicians are sharpening new algorithms—open-source tools, developed over recent years—that detect and counter gerrymandering, the egregious practice giving rise to those bestiaries, whereby politicians rig the maps and skew the results to favor one political party over another. Republicans have openly declared that with this redistricting cycle they intend to gerrymander a path to retaking the US House of Representatives in 2022.
The term “gerrymander” dates to 1812, when a Massachusetts district drawn to the advantage of Governor Elbridge Gerry was so strangely shaped that it was likened to a salamander. Thus, to “gerrymander” is to manipulate district boundaries with a political agenda, and thereby manipulate election outcomes.
The use of computers to generate and gerrymander electoral maps became relatively common in the 1990s, although early redistricting software was prohibitively expensive, costing $500,000 to $1 million. Now the industry standard is Maptitude, made by Caliper. When the first Maptitude for Redistricting package was released, in the late 1990s, it cost $2,999. The current price ranges from $1,000 to $10,000, depending on the user’s needs.
That the technology had advanced by leaps and bounds since the previous redistricting cycle only supercharged the outcome. “It made the gerrymanders drawn that year so much more lasting and enduring than any other gerrymanders in our nation’s history,” he says. “It’s the sophistication of the computer software, the speed of the computers, the amount of data available, that makes it possible for partisan mapmakers to put their maps through 60 or 70 different iterations and to really refine and optimize the partisan performance of those maps.”
As Michael Li, a redistricting expert at the Brennan Center for Justice at the New York University’s law school, puts it: “What used to be a dark art is now a dark science.” And when manipulated maps are implemented in an election, he says, they are nearly impossible to overcome.
“The five justices on the Supreme Court are the only ones who seemed to have trouble seeing how the math and models worked,” says Li. “State and other federal courts managed to apply it—this was not beyond the intellectual ability of the courts to handle, any more than a complex sex discrimination case is, or a complex securities fraud case. But five justices of the Supreme Court said, ‘This is too hard for us.’”
“They also said, ‘This is not for us to fix—this is for the states to fix; this is for Congress to fix; it’s not for us to fix,’” says Li.
Will it matter?
As Daley sees it, the Supreme Court decision gives state lawmakers “a green light and no speed limit when it comes to the kind of partisan gerrymanders that they can enact when map-making later this month.” At the same time, he says, “the technology has improved to such a place that we can now use [it] to see through the technology-driven gerrymanders that are created by lawmakers.”