Traditionally, three broad categories of electoral systems have been described: plurality systems, majority systems, and proportional representation systems. The most important element that differentiates these electoral systems from one another is the means by which seats in the legislature are allocated:
- to candidates receiving a plurality of the vote
- to candidates obtaining a majority of the vote
- proportionally on the basis of votes cast for political parties or candidates
A recent addition to these three broad categories of electoral systems is the mixed electoral system, which combines elements of both proportional representation and plurality or majority voting systems.
Delimiting Districts: Plurality or Majority Systems
The delimitation of electoral districts is most commonly associated with plurality or majority electoral systems. Both systems tend to rely heavily, if not exclusively, on single-member electoral districts. These districts must be redrawn periodically to reflect shifts in the population. Both systems also share one fundamental element because of their reliance on single-member districts--the number of seats that a political party receives depends not only on the proportion of the votes it received, but also on where those votes were cast. Under plurality and majority systems, minority political parties whose supporters are not geographically concentrated usually obtain fewer seats than their proportion of the vote would suggest they are entitled. The multimember districts of proportional systems can rectify this distortion in the transfer of votes to seats because the larger the magnitude of the electoral districts, the more proportional the results.
The process of electoral district delimitation in a plurality system is important because the configuration of districts can affect the partisan, and possibly even the racial, ethnic, religious or linguistic composition of the legislature. The effect may be intentional, as in a partisan "gerrymander," or it may be unintentional. Even district boundaries drawn by a neutral boundary commission may unintentionally favour one party over others.
Majority electoral systems can, and do, produce election outcomes that are just as disproportional as plurality electoral systems with regard to the ratio of seats to votes. This is not surprising, given that both systems rely almost exclusively on single-member districts. The district delimitation process in a majority system is, therefore, just as important as it is in a plurality electoral system.
For more information on plurality or majority electoral systems see the Electoral Systems: Plurality/Majority Systems.
Delimiting Districts: Proportional Representation
There are two major types of proportional representation systems: the party list system and the single transferable vote. (The mixed member proportional system also produces proportional results, but this system will be discussed under the "mixed system" category.) The party list system is the far more common of the two. Under the party list system, electoral districts rarely, if ever, require delimitation. If electoral districts are employed, they are relatively large multimember districts whose boundaries generally correspond to administrative divisions. To accommodate shifts in population, the number of seats allocated to individual multimember districts is adjusted, rather than redrawing the boundaries of the districts. The single transferable vote, used in Ireland and Malta, is the other type of proportional representation. Because voting is on the basis of candidates, not parties, these countries employ small multimember districts with only three to five members elected per district. Electoral district boundaries must therefore be redrawn periodically in these two countries.
Delimiting Districts: Mixed Electoral Systems
Mixed electoral systems are becoming increasingly popular. They employ both party list proportional representation and single-member electoral districts with plurality or majority vote requirements. The German electoral system is the prototypical mixed electoral system.
Because mixed systems incorporate single-member districts, the delimitation of electoral districts must occur periodically to adjust for shifts in the population. The importance of the delimitation process and the influence that district configurations have on the outcome of elections is dependent on whether party list seats are used to correct any distortions in the relationship between seats to votes produced by the single-member districts. In countries such as Germany, seats allocated under the party list system are used to compensate for any distortions in the seats-to-votes ratio produced at the electoral district level. Mixed systems that use party list seats in a compensatory manner are sometimes called "mixed member proportional" systems because the election results are proportional.
In countries such as Russia, party list seats are not used to compensate for any disproportionality arising from elections in single-member districts. Rather, seats allocated to the parties under the party list component of the election are simply added to the seats won at the electoral district level. The partisan seats-to-votes ratio may therefore be distorted. In this type of mixed system, sometimes called a "parallel" system, the district delimitation process is more important because it can have a more pronounced effect on the partisan composition of the legislature.
