In the United States, the responsibility for drawing congressional district lines lies with state legislatures. This process, known as redistricting, occurs every ten years after the census. States may allow their governing bodies to adjust district boundaries to reflect population changes. However, this power can lead to gerrymandering, where boundaries are manipulated to favor one party over another. Some states have introduced independent commissions to create fairer district maps, aiming to increase the integrity of elections and enhance political representation.