There were some cases that were handled by the Warren Court that dealt with reapportionment. Baker v Carr and Reynolds v Sims were very important cases.
In the 1962 Baker v Carr decision, the Supreme Court ruled that while the legislature was responsible for drawing legislative district boundaries, the courts could review these boundaries. In this case, the boundaries in Tennessee were drawn in such a way that they favored those who lived in rural areas. Rural regions had more representatives per person than the more populous urban areas had.
In the 1964 Reynolds v Sims case, the Supreme Court ruled that when legislative boundaries or districts are created, they should reflect the concept of “one person, one vote.” In this case, Alabama’s legislative districts were based on the population from the 1900 census. This ignored the growth of the population in urban areas and created a situation where “one person, one vote” didn’t really exist. Those people who lived in the rural areas were favored by using the 1900 census to determine legislative districts.