Electoral District - District Magnitude

District magnitude is the number of representatives elected from a given district to the same legislative body. A single-member district has one representative, while a multi-member district has more than one. Voting systems that seek proportional representation (such as the single transferable vote) inherently require multi-member districts, and the larger the district magnitude the more proportional a system will tend to be (and the greater the number of distinct parties or choices that can be represented.). An exception is when a multi-member districts uses the winner-take-all method to select the representative, as is the case with Singapore's Group Representation Constituency.

Under proportional representation systems, district magnitude is an important determinant of the makeup of the elected body. With a larger number of winners candidates are able to represent proportionately smaller minorities; a 10% minority in a given district may secure no seats in a 5 member election but would be guaranteed a seat in a 9 member one because they fulfill a Droop quota.

The geographic distribution of minorities also affects their representation - an unpopular nationwide minority can still secure a seat if they are concentrated in a particular district. District magnitude can sometimes vary within the same system during an election. In the Republic of Ireland, for instance, national elections to Dáil Éireann are held using a combination of 3, 4, and 5 member districts. In Hong Kong, the magnitude ranged from 3 to 5 in 1998, when the current electoral system was introduced for Legislative Council geographical constituency elections, and will range from 5 to 9 in the forthcoming election in September 2012.