Biproportional apportionment

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Biproportional apportionment is a proportional representation method to allocate seats in proportion to two separate characteristics. That is, for two different partitions each part receives the proportional number of seats within the total number of seats. For instance, this method could give proportional results by party and by region, or by party and by gender/ethnicity, or by any other pair of characteristics.

1. Example: proportional by party and by region
   • Each party's share of seats is proportional to its total votes.
   • Each region's share of seats is proportional to its total votes
     • (or this could be based on its population-size or other criteria).
2. Then, as nearly as possible given the totals for each region and each party:
   • Each region's seats are allocated among parties in proportion to that region's votes for those parties. (The region's seats go to locally popular parties.)
   • Each party's seats are allocated among regions in proportion to that party's votes in those regions. (The party's seats are in regions where it is most popular.)