The Equal Protection Clause of the Fourteenth Amendment to the United States Constitution has been interpreted by the United States Supreme Court to require the States to draw legislative districts so that each district is about the same size in population as the others. In a case decided in 1964, the U.S. Supreme Court stated that the "overriding objective must be the substantial equality of population among the various districts." (Reynolds v. Sims, 377 U.S. 533). This is known as the "one-person, one vote" rule.
Historically, from the 1960s until the early 2000s, the U.S. Supreme Court developed an allowable deviation in state legislative redistricting that was called “The 10% Rule.” In a series of cases following the Reynolds case, the Supreme Court effectively established a threshold of a 10% population variation between districts for legislative redistricting. If a state drew all its districts within 10% of each other in population size then the courts generally would presume that the state’s district map passed muster under the one-person, one-vote standard. If variations between districts exceeded 10% then the redistricting plan would not be upheld unless the state proved that such a disparity was justified by extraordinary circumstances.
There is a presumption that if a state’s largest and smallest districts are more than 10% apart, the redistricting plan is not constitutional. However, meeting the 10% target is not necessarily sufficient—for example, districts may be found to have been drawn unconstitutionally if there is evidence of wrongful intent, even when the difference is less than 10%. Examples of wrongful intent include discrimination based on race or ethnicity, attempting to protect or disadvantage an incumbent, bribery, or attempting to minimize the voting impact of one community of interest at the expense of another.
The Supreme Court has ruled that when drawing state and local legislative districts, states may deviate somewhat from perfect population equality to accommodate traditional districting objectives, among them:
- Complying with the Voting Rights Act;
- Preserving the integrity of political subdivisions;
- Maintaining communities of interest;
- Creating geographic compactness and contiguity; and
- Accommodating geographical barriers (e.g., national forests, military reservations, lakes, roadways, and rivers).
However, these are guidelines, not hard and fast rules. Counties and cities have meandering boundaries along highways and rivers and are not compact. Municipal boundaries may cross county lines. Community of interests must be identifiable and concentrated. Racial and language-based minority interests must be protected under federal law. All of these guidelines necessitate sound judgment, and the courts recognize that redistricting bodies must occasionally use discretion in such situations.
Determining the variance:
Courts have approved the use of a statistical measure called the overall range to determine whether a redistricting plan meets the population equality standard set out above. The overall range is a measure of inequality between districts. In Arkansas, the overall range will be determined as follows:
- First, the Board of Apportionment will determine the population limits for districts in Arkansas by dividing the total state population by the number of seats in each house of the General Assembly, separately, to determine the average district size for each house.
- The total population divided by the 35 senate seats equals the average senate district size.
- The total population divided by the 100 house seats equals the average house district size.
- After the districts are redrawn, the total variance for each house is determined by measuring the percentage difference in population between the largest population district and the average district (for example, 5%), and the smallest population district and the average district (for example, 3%), and then adding the percentage differences together (8%). This is the overall range, and it provides a thumbnail sketch of the equality of population distribution.