In the United States (US), the legislative branch of government is responsible for creating and passing laws that represent the interests of the people. At both the federal and state levels, this legislative branch typically takes a bicameral, or two-chambered form. The upper chamber is known as the senate. Each senator represents a senatorial district, or region, and is elected by the people who live in that region. While senatorial districts at the federal level are simply based on state lines, a senatorial district within an individual state must be calculated based on population distribution rather than geographical borders.
Each US state is permitted to send two senators to the US Senate, regardless of the size or population of the state. In this case, the senatorial district encompasses the entire state, and is not affected by population distribution. Members of the other legislative branch, the US House of Representatives, are elected by the citizens of their congressional district. These districts are determined based on populations within the state, and the number of representatives varies based on relative state population. This means that each state has only one senatorial district, but may have dozens of congressional districts.
Forty-nine of the states also have a bicameral legislative branch at the state level, consisting of both a state house and state senate. Nebraska has just one branch, known as the senate. The senate within each state can vary in size from fewer than 20 members to more than 60, depending on the laws of that state. Unlike federal Senators, who serve six-year terms, state senators serve terms ranging from two to four years.
Prior to 1964, states set their own senatorial districts based on arbitrary factors, such as county lines. In the early 1960s a series of lawsuits were heard by the US Supreme Court regarding senatorial district determination criteria in Alabama. Those who filed the suits argued that suburban voters were over-represented, while urban voters were under-represented within a state senate due to the way the senatorial districts were determined.
In the landmark 1964 case of Reynolds V. Sims, the court determined that each state must set senatorial districts based on population distribution, not county lines. The justices wrote in their decision that elected leaders must represent people, not areas of land. This had a profound effect on state governments, and led to major changes in the way districts and representation were determined within each state.