District magnitude refers to the number of representatives returned (or elected) from a district. As the district magnitude increases so does the proportionality of the result. If the district magnitude is too large, then the number of candidates and the size of the ballot paper can become unmanageable. For large representative bodies, such as State & Federal parliamentary chambers, PRSA policy is to advocate for a gold standard district magnitude of 5 or 7.
To be elected from a 5-member district, a candidate only needs to obtain 16.6% of the vote. This delivers good proportionality, ensuring that the views of the elected representatives reflect the views of the people who elect them.
For smaller bodies, such as Local Government Councils, 7-member districts function well in regional areas, but less well in metropolitan areas, where they attract too many candidates and an overly large ballot paper. Also, 5- and 7-member districts only permit Councils of 5, 7, 15 or 21 members (assuming a maximum Council size of 21), which is not flexible enough. Therefore, for smaller representative bodies the gold standard includes an option for 3 members per district. This enables Councils of 5, 7, 9, 15 or 21 members.