Congress of the United States - Apportionment

Seats in the Senate are apportioned, or distributed, evenly across the states, with each state receiving two. Seats in the House of Representatives are apportioned between the states on the basis of population, with the most populated states receiving the most representatives and no state receiving less than one. The Constitution requires that a census be conducted every ten years in order to determine the number of seats allotted to each state. An apportionment method called equal proportions is used so that no state will receive less than one member.

The Constitution does not mandate that states having more than one representative be divided into congressional districts, although a state legislature can make such a division. States cannot apportion congressional districts on a discriminatory or unreasonable basis.