Many Americans believe that someone, somewhere in Washington, must be in charge of tracking who is and who isn’t a citizen of the United States. Apparently, so does the U.S. Supreme Court, which just accepted a voting rights case that turns on the government’s ability to count the number of citizens in each voting district. But despite all the talk these days about government and Big Data, the justices, like the rest of us, might be surprised to learn that the most basic information as to who is an American citizen cannot actually be found in any publicly available government data set — anywhere. The case, Evenwel v. Abbott, poses a question: whether the Constitution’s long-standing “one person, one vote” principle requires equal numbers of voters per district instead of equal numbers of people, as is current practice. Most commentary on the case has focused on its implications for political parties and racial groups. But focusing on the politics, or even on the merits of the constitutional argument, ultimately distracts from a much bigger problem: The data necessary to draw districts with equal numbers of eligible voters does not exist. We have no national citizen database that tells us how many citizens live in each district around the country.
“What about the U.S. Census?” you might be wondering. It’s true that the census releases a data set that provides the building blocks of redistricting plans for Congress, state legislatures, city councils and school boards. But that data set counts just two things: the total number of people, and the number of people over the age of 18, in every community in the country. The data file has no information about which of those people are citizens and which are not. Voter registration lists, another alternative, are notoriously unreliable and highly variable depending on whether an election is coming up — and some states don’t keep track of voter registration at all.