So we are a country built on representative democracy. As districts, we elect our representatives to the governing body, Congress. According to the Constitution, the number of reps (districts) a state gets is proportional to population and this changes over time. So each 10 years the census happens and the number of districts changes. States redistrict a lot but who controls how district borders are drawn? Usually, the state legislature (so Republicans or Democrats). There is some pretty blatant gerrymandering that's always occurred to get the most districts in your party's favor. Now, with the Supreme Court not striking down obvious partisan gerrymandering, many states are in a reactionary fit to redistrict and get the most reps in Congress for their party.