Reapportionment / Redistricting Information & Maps
The United State Constitution established apportionment in Article I, section 2. It was amended (AMENDMENT XIV - Section 2) in 1868:
"Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, excluding Indians not taxed. But when the right to vote at any election for the choice of electors for President and Vice-President of the United States, Representatives in Congress, the Executive and Judicial officers of a State, or the members of the Legislature thereof, is denied to any of the male inhabitants of such State, being twenty-one years of age,* and citizens of the United States, or in any way abridged, except for participation in rebellion, or other crime, the basis of representation therein shall be reduced in the proportion which the number of such male citizens shall bear to the whole number of male citizens twenty-one years of age in such State".
What is Reapportionment?
apportion (verb) - to divide, distribute, or assign appropriate shares of; allot proportionally Source: thefreedictionary.com
Video by the U.S. Census
The Reapportionment Act of 1929 established a permanent method for apportioning a constant 435 seats in the U.S. House of Representatives according to each census. All 50 states have one seat and the remaining 385 seats are distributed, using a formula, to states appropriate to its population.
Since the 1940 census, seats have been divided in equal proportions and apportionment is a fundamental reason for the census.
See comparison of current to 2012 Congressional Map