This website explains how the Iowans reaportion their legislative and congressional districts. It concludes:
“Gerrymandering is having a profound impact on the political process.  The practice sharply reduces the number of competitive elections to the US House of Representatives. For example, in 2002, only four challengers were able to defeat incumbent members of Congress, the lowest number in modern American history, according to political scientists Norman Ornstein and Thomas Mann.Non-competitive districts lead to entrenched, polarized legislatures. Incumbents fear primary challenges from even-more-extreme partisans, not the other party, as a result of their “safe” districts.
By contrast, the non-partisan redistricting process has helped move politics in Iowa back toward the center. Most Iowa politicians know they must appeal not only to their party, but also to independent voters and voters affiliated with the other party. This inevitably leads to an emphasis on bipartisan cooperation and the public’s best interest.”
“
