Every decade, following the release of decennial census data and the reapportionment process, state legislatures and committees redraw district boundaries to account for population changes. This process is called redistricting. As of 2010, there were 43 states with at least two congressional districts, meaning that they must undergo a redistricting process.
Two federal guidelines govern redistricting. Both of them are based on demographic data: equal population in each district and the protection of racial/ethnic voting rights.
These are the only mandatory guidelines. States can develop additional standards to guide the redistricting process. These include requirements to:
Only five states—Arizona, California, Idaho, Rhode Island, and Washington—have guidelines addressing all of these issues; another 19 have guidelines addressing at least one of these issues. North Carolina is one of 19 states whose congressional process is guided solely by the federal criteria.
In keeping with the standard of “one person, one vote,” every congressional district is supposed to have equal population after redistricting. Equal population across districts is referred to as ideal population size and is required “as nearly as is practicable.”
There is typically strict enforcement of equal population requirements for congressional districts. Earlier Supreme Court decisions showed no tolerance for slight deviations from ideal district size. Based on these precedents, and the capacity of computer-based redistricting software to draw precisely equal districts, district populations frequently differ by no more than one person. However, the Court’s recent decision in Tennant v. Jefferson County Commission suggests that strict adherence to equal population may not be required if the state can prove “population deviations [are] necessary to achieve legitimate state objectives, such as avoiding contests between incumbents and not splitting political subdivisions.”
Because districts are redrawn only once every decade, population changes over the prior 10 years often create a need for significant shifts in district boundaries, even if no new House seats are apportioned to the state.
Federal requirements in Section 2 of the Voting Rights Act of 1965 guard against efforts to dilute the impact of racial and ethnic minority voters. Typically, action is taken to protect racial and ethnic minority groups that are geographically compact, vote for the same types of candidates, and have faced (or currently face) discrimination. In redistricting, this works to limit practices commonly referred to as packing and cracking.
Packed districts are drawn to produce high concentrations of minority voters in a single district. This allows minority groups to elect the candidate of their choice in this district, but limits minority influence in other districts. Cracked districts split minority voters across electoral districts, effectively limiting their ability to influence the outcome of a single election.
In practice, this has led states to draw “majority-minority” districts to prevent minority vote dilution. Although there are no specific criteria pertaining to the number of majority-minority districts required to prevent vote dilution, there is some emphasis on proportionality. That is, the number of majority-minority districts should be “roughly proportional to [minority group] shares in the voting age population.” For the past two decades, North Carolina has had two majority black congressional districts (the 1st and the 12th).
Majority-minority districts are not without controversy (cf. Shaw v. Reno, challenging the constitutionality of North Carolina’s 12th district). Supporters of majority-minority districts argue that they are necessary to reduce political disenfranchisement and increase political opportunities for minorities. Others argue that they effectively pack minority voters into districts, with implications for partisan politics. Articulating the tension between these two viewpoints in The Realities of Redistricting, Jonathan Winburn notes:
The partisan impact of majority-minority districts has received much attention over the past decade with two primary schools of thought emerging. The first is that racial gerrymandering is generally an indirect cause of Democratic losses and that Republican gains have occurred independent of redistricting. The second, more compelling finding, is that by packing black voters into majority-minority districts more minorities benefit to the detriment of the overall success of the Democrats. In this scenario, the Republicans benefit greatly from majority-minority districting as the packing of minority voters, who traditionally are strong Democratic voters, into a few concentrated districts allows Republicans to gain more seats overall.
Although North Carolina has additional state guidelines for the state legislative redistricting process, federal guidelines—equal population and protection of racial/ethnic minority voting rights—are the only guidelines governing the congressional redistricting process in North Carolina and 18 other states. While these are based on demographic data, their implementation and interpretation are rooted in a complex legal history that continues to evolve.
11/11/2015 Update: New York state was changed on the map to reflect redistricting legislation passed in 2014.