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The “One Person, One Vote” rule requires that each district in a single-member district election system contain an equal number of people. This rule is also called the “no malapportionment rule.” Under this rule, the geographic size of a district does not matter; instead, it is the population size that is important. The U.S. Supreme Court has stated the rationale for this rule as follows:

Legislators represent people, not trees or acres. Legislators are elected by voters, not farms or cities or economic interests. As long as ours is a representative form of government, and our legislatures are those instruments of government elected directly by and directly representative of the people, the right to elect legislators in a free and unimpaired fashion is a bedrock of our political system.

The one one person, one vote rule did not take effect until the 1960s. Prior to then, when states and local governments divided up political power, they did not have to consider the number of people being represented in each district, and districts had very different population sizes. Unequal representation exaggerated the voting power of some and minimized the voting power of others.

Prior to 1962, federal courts could not address malapportionment issues because they were considered issues solely for the legislature to decide. In 1962, the U.S. Supreme Court decided that federal courts could address malapportionment issues. Subsequently, the U.S. Supreme Court ruled that the 14th Amendment’s guarantee of “equal protection of law” was violated when a small number of people in one district enjoyed the same political power as a large number of people in another district. Every person’s vote must count equally: One Person, One Vote. This rule applies both to congressional districts (through Article I, Section 2 of the U.S. Constitution) and to state and local election districts (through the 14th Amendment to the U.S. Constitution).

Application of the “One Person, One Vote” Rule: This rule has implications for congressional, state, and local levels.

Congressional Level: The “congressional district rule” requires strict equality of population for each congressional district. is rule comes from Article I of the U.S. Constitution, and it requires congressional districts to be “as mathematically equal as reasonably possible.”

State and Local Levels: State legislatures and local governing bodies (including county and city governments and school boards) must also comply with the one person, one vote rule, but they are permitted more leeway than allowed for congressional districts. State and local governments are required to make an “honest and good faith” effort to provide for an equal population distribution in each district. They can have an overall deviation of up to ten percent with little, if any, justification. If the overall deviation exceeds ten percent, then the state or local government must justify the deviation “based on legitimate considerations incident to the effectuation of a rational state policy.” If the overall deviation is greater than 16.4 percent, the plan will likely fail, regardless of any justification.

To determine whether districts comply with the one person, one vote rule, the population of each district is compared with the “ideal population.” The “ideal population” equals the total population of the jurisdiction divided by the number of districts. The “overall deviation” equals the population of the largest district minus the population of the smallest district. If this number is greater than ten percent of the population, then the state or local government must provide a justification.

* The text above was excerpted from Chapter Four of “Drawing The Line” from the Southern Poverty Law Center.