Every 10 years the U.S. Census Bureau conducts a census of the population of the United States. One of the primary purposes of the census is to divide states up into districts so "we the people" are equally represented in our government. At least every decade, the districts are reevaluated to make sure that everyone has a voice. Sometimes, redistricting is done more often than every 10 years. Redistricting happens at all levels - from the U.S. House of Representatives (for states with more than 1 representative) to your state and sometimes to your city or county governments.
State laws govern how each state redistricts.
While the law does not provide a checklist of criteria, the Constitution and the Voting Rights Act provide principles that are expected.
Some criteria have been added since 2000 and adopted by some but not all states:
This is easy - the entire state is our district. Since we only have one representative, there is no need for districts. If we gained population, this could change based on the decennial census. There are 435 seats in the House of Representatives. Each state is guaranteed 1 seat but beyond that, the seats are given based on population.
There are 35 districts that make up the South Dakota legislature. Each district has one senator and two representatives. The districts are drawn by the state legislature in South Dakota. Districts can only be drawn up after the decennial census. The 2020 census will lead to redistricting activities in 2021 and new district boarders in the 2022 election.
In 2011, the legislative committee responsible for redistricting held a series of public meetings.