District magnitude refers to the number of legislative seats assigned to a district. Countries have adopted electoral rules that range anywhere from the exclusive use of single-member districts to a system where the entire country, in effect, functions as a single district. The United States and the United Kingdom are at one end of the spectrum, in which each and every legislator represents a single district. At the other end of the spectrum are countries such as Israel and the Netherlands, in which the district magnitude is equal to the total number of members of the legislature. Most countries are somewhere in the middle of this range; and within a country there is often a wide variation in the magnitude of districts.
Some countries set all their electoral districts at the same magnitude or within some narrow range of magnitudes. District boundaries are then usually drawn according to some voters-per-representative formula. This approach has been adopted in the United States and most other countries with plurality or majority electoral systems, where the district magnitude is set at one. This procedure is also used in Ireland and Malta, both of which employ small multimember districts and the single transferable vote. In Malta, all districts have a magnitude of five. In Ireland, the range in magnitude is from three to five.
Alternatively, some countries use existing regional, administrative or political divisions as electoral districts. Each electoral district is then assigned a specific number of seats according to its population. Most countries with electoral systems based on proportional representation use this procedure. The larger the district magnitude, the more proportional the outcome of the election--that is, the more seats per district, the closer the approximation between a political party's percentage of the vote and the number of seats that party receives in the legislature.
Single-member electoral districts must be redrawn periodically to ensure relatively equal populations. Some countries with uniformly small multimember districts must also redistrict periodically in order to comply with equal population standards. Electoral districts with large magnitudes, however, do not need to be redrawn; seats are simply reassigned from one district to another to meet equal population standards.
