Wesberry v. Sanders
Wesberry v. Sanders, 376 U.S. 1 (1964) was a case involving congressional districts in the state of Georgia, brought before the Supreme Court of the United States. The Court issued a ruling on February 17, 1964 that districts have to be approximately equal in population.
A related case was Reynolds v. Sims, 377 U.S. 533 (1964), which held that districts for state senate seats had to be roughly equal in population.