Political district determination using large-scale network optimization

Political redistricting involves the amalgamation of a large number of geographic or statistical units into a smaller set of electoral districts such that the districts satisfy various criteria prescribed by law, judicial mandate, or historical precedent. This paper describes a network-based optimization model that is currently being used by governmental decision-makers in New Zealand to assist in the preliminary stages of determining Parliamentary district boundaries. The model is capable of solving large-scale problems. In the New Zealand case, the procedure has been applied to problems involving over 35,000 geographic units (called ''meshblocks'') and 95 Parliamentary districts. The model generates electoral districts that have roughly equal population and are generally compact in shape. One of the key features of the model is its flexibility. On the one hand, it can take into account currently existing features such as topographic terrain or previously existing electoral boundaries. On the other hand, it can also be used to generate an entirely new set of political boundaries as was mandated by the voters in a recent referendum in New Zealand. (C) 1997 Elsevier Science Ltd.