With examples, thanks.
In: 9
Let’s suppose we have a city with 1 million people, and a city council of 10. We could divide them one of two ways:
In the “first-past-the-post” system, we divide the city into 10 districts of 100 000 people, and have each city council person represent one district. In an election, you run for city council in your district, and whoever gets the most votes in each district wins that seat.
As an example, if you, me, and the ModBot run in our district, and I get 40K votes and change, you get 35K votes and change, and the ModBot gets just under 25K votes; I got the most votes, so I get the seat. The same thing repeats over all ten districts; with the ten winners making up the city council.
In the “proportional representation” system, you have “parties” create “lineups” – basically a list of who they want to be on the council. Then, all 1 million people vote on which party they want to win. Each party gets 1 seat for every 100 000 votes they have; and then the leftover seats get distributed based on some system. Normally, the way they do this is to divide the number of votes each party got by 1 more than the seats they already have (parties with no seats get divided by 1), and the parties with the most divided votes get the remaining seats.
As an example, my party, your party, ModBot party, and UselessExplanations party all run. My party gets 375K votes, your party gets 325K votes, ModBot Party gets 220K votes, and UselessExplanations gets 80K. 8 council seats are easy: my party gets 3, your party gets 3, and ModBot gets 2. We now divide votes by (seats+1), leaving me with (375K votes divided by 4) 94K for the last two seats, you with (325K divided by 4) 81K for the last two, ModBot with (220K divide by 3) 73K votes for the last two, and UselessExplanations with 80K votes – the top two are my party and your party; so the final council has the first four people from my list, the first four from your list, and the first two from ModBot’s list.
Some systems might divide things differently – I know some give extra weight to parties without any representation; so in that case, your fourth seat would instead go to UselessExplanations, giving them one seat.
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First past the post has the advantage of being (usually) easier to understand; and tends to support voting for individuals rather than parties. However, it has the problem of being vulnerable to “gerrymandering”, or dividing districts up in a way that favors one group over another. It also tends to result in two-party systems; because going back to the example, if ModBot’s supporters preferred you over me, they would have been better off voting for you instead of ModBot – and over time, it turns out to be pretty easy for two parties to get into a position where they both serve their own interests and only superficially support the popular interest.
Proportional representation requires officially recognizing parties, and can take more work to work out all of the rules and what to do in interesting circumstances (things like parties kicking representatives out after voting); but tends to give people more options without penalizing them for supporting those options.
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