In which election process is filling a seat based on the population of each state

The election process that fills a seat based on the population of each state is the election for members of the House of Representatives in the United States. The House of Representatives is the lower chamber of the U.S. Congress, and seats are allocated to each state based on its population as determined by the decennial census. Each state is guaranteed at least one seat, and the remaining seats are distributed among the states based on population.