Electorate graphs adjusting for redistributions

Electorate boundaries often change with redistributions. Over two decades they may change substantially.

To calculate how a particular seat as it is constituted today would have voted in, say, 1984, would ideally involve going back and adding up all votes per polling place.

This would be very hard to do.

A second best option is to, in each electorate, start with the notional two party preferred vote today, and successively subtract the swing at each previous election. These swings are calculated (by the AEC or others) from estimated notional two party preferred votes before elections, and actual votes afterwards.

This is what I do. It's not as good as going back and recounting votes, but it is a second best option.