Enumeration and sampling analysis of Montana’s 2020 congressional redistricting map

The 2020 decennial census data resulted in an increase from one to two congressional representatives in the state of Montana. The new districts nearly followed county lines and provide a rare instance of an enumerable redistricting problem. We use the enumerated set of maps to analyze the redistricting process and compare the adopted congressional map to the space of all other possible maps, the full set of 1-person deviation maps and several ReCom (spanning tree) generated ensembles. Along with considering the usual selection of statistics on these maps (population deviation, compactness, minority representation and political outcomes) we look at Montana’s definition of competitive districts and analyze the best ER upper bound for the ReCom algorithm in this simple case.