Measuring a Gerrymander

There is no such thing as a fair or non-partisan districting plan. Whether intentionally or blindly, such plans involve political choices and have critical effects on the political parties. The various "proposed public interest criteria for redistricting...are not neutral, they are not grounded in broader principles that command general assent, and in many cases they are incoherent and cannot be made to work." Because reapportionment is inherently political, some way to identify or measure its political effects is needed in selecting a districting plan. Yet there are few concrete measures of what is often called a gerrymander, "electoral districts [which] result, or are thought to result, in partisan advantage." The main difficulty in gauging a gerrymander is in finding a coherent basis of comparison; to evaluate a districting proposal's political effects, it is crucial to establish some sort of context in which to do so. One such context is to locate the natural limits, the upper and lower bounds, within which a gerrymander may take place. Since the gerrymanderer cannot change the way people vote or where they live, these demographic factors constrain his efforts by providing a fixed upper limit, a perfect gerrymander. A perfect gerrymander is defined as