Our discussion of gerrymandering became a discussion of voter initiatives, since that is generally the only way that states adopt nonpartisan redistricting commissions–legislatures don’t do it, usually.  There are a lot of states that allow voter initiatives, but they are mostly in the west.  An excellent source of information on which states allow them, with a state by state compilation of the rules that apply to them, is a website published by the University of Southern California Initiative & Referendum Institute . There is also a useful Wikipedia article.