United States congressional apportionment is the process by which the 435 seats in the United States House of Representatives are distributed among the 50 states. Gains and losses, appearing in the map, refer to changes between the 2000 and 2010 apportionments. The power shift took effect starting with the 2012 U.S. election.
Well informed U.S. residents respond to the Census every ten years. Census Bureau data determines how power and money are distributed to the fifty states.
If you live in the United States, and have not yet responded to the 2020 Census, you can get more information here. The Census Bureau is no longer collecting data from the population.