WASHINGTON (AP) — Every 10 years, states must redraw the boundaries of congressional districts to account for population changes in the new census. Some states add House districts, while others lose them, but the total stays at 435.
Following the 2010 Census, eight states gained seats. Arizona, Georgia, Nevada, South Carolina, Utah and Washington each added a seat. Florida added two and Texas added four.
Ten states lost seats. Illinois, Iowa, Louisiana, Massachusetts, Michigan, Missouri, New Jersey and Pennsylvania each lost one. New York and Ohio each lost two seats.
The rest of the states stayed the same, but they still had to draw new boundaries to reflect population changes due to people moving, multiplying or dying.
The exceptions were the seven states with only one House district: Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont and Wyoming.
The decennial census is done at the start of each decade, so redistricting is done for the next election. The latest census was in 2010, so new districts were drawn in time for the 2012 congressional elections.
There are two hard-and-fast federal rules for drawing district boundaries: All districts within a state must have about the same number of people, and states cannot draw districts that dilute the voting strength of minority voters under the Voting Rights Act.
Drawing odd-shaped districts for political gain is OK, the Supreme Court has indicated, as long as those two rules are not violated.
"The court has never blessed blatant partisan gerrymandering, but it hasn't struck it down," said Justin Levitt, a law professor at Loyola Law School in Los Angeles. "So for practical purposes, partisan gerrymandering is OK."
The first rule on size is pretty straightforward, though there are disparities among states. For 2010, the average congressional district had 710,767 people, according to the Census Bureau. Montana had the largest, at 994,416 people. Rhode Island had the smallest, at 527,624 people.
The rule on following the Voting Rights Act is more complicated. The Supreme Court has ruled many times on the issue. In general, experts say a state's districts cannot be drawn to prevent minority voters from electing candidates of their choice. That usually means if you can draw a geographically compact district with enough black or Hispanic voters to elect a black or Hispanic candidate, you have to do it. If you split those voters into two or more districts, hurting their ability to elect minority candidates, you will invite a court challenge under the Voting Rights Act.
Many states also have criteria for drawing districts, saying they should be geographically compact or follow local political boundaries. But, as Levitt points out, "In most states, these standards must be followed only as closely 'as is practicable,' leaving substantial flexibility."
— Stephen Ohlemacher
State criteria: http://redistricting.lls.edu/where-tablefed.php