1. John F. Nagle is a professor emeritus of physics and biological sciences at Carnegie Mellon University in Pittsburgh, Pennsylvania, USA. Alec Ramsay is principal at Dave's Redistricting in Seattle, Washington, USA. We thank B. Grofman, J. Cervas, M.D. McDonald, G. King, G.R.J. Wallin, S.-H. Wang, M. Duchin, N. Stephanopoulos, E. McGhee, and G.S. Warrington for informative discussion. We especially thank Stephen Wolf, whose data made this study possible.