The New York Times has an interesting story on the parties efforts to redistrict congressional seats throughout the nation.
Washington state's recent gain of a congressional seat means somewhere in the country another state will lose a seat. The additional seat(s) given to states in the South and West due to increases in population numbers will be off-set by the loss of seats in states from the Mid-west and East Coast region.
The Times also reports many of the decision makers involved in determining the congressional district lines have a lot of new friends. In Washington, the congressional district lines will be determined by a Redistricting Commission comprised of two Democrats and two Republicans selected by the legislative caucuses and a chairperson selected by those four commissioners.
More information can be found on the commission website although it needs to be updated once the new commission is officially selected.