Reapportionments normally occur following each decennial census, though the law that governs the total number of representatives and the method of apportionment to be carried into force at that time are enacted prior to the census.

Why is apportionment important?

Apportionment is one of the most important functions of the decennial census. Apportionment measures the population so that seats in the U.S. House of Representatives can be correctly apportioned among the states. ... The Constitution does not specify a certain method of apportionment.

What action causes reapportionment?

The Constitutional basis for conducting the decennial census is to reapportion the U.S. House of Representatives. Apportionment is the process of dividing the 435 memberships, or seats, in the U.S. House of Representatives among the 50 states.