SA redistribution – final map and margins

The final boundaries for the South Australian state electoral redistribution were released in November, and I have just finished producing my new map of the electoral boundaries, as well as my estimates of the margins.

The map is shown below:

The boundary changes were slightly less dramatic than the draft boundaries, with boundaries reverting to the 2018 map in a number of places. Overall 18.1% of voters have been moved to a new seat, down from 19.7% on the draft boundaries.

I have produced estimates of the margin in each seat. No seats changed hands in the redistribution, but there were some dramatic changes.

Less than 60% of voters in the new seats of Florey, Reynell, Playford and Hurtle Vale were already in that seat. Only 48.8% of voters in Stuart have stayed still, and just 36.5% of voters in Frome were already in that seat. Those biggest changes were due to Port Pirie being moved from Frome into Stuart. This was a knock-on effect from all of the electorates in the north of the state being too small, which resulted in Port August being split between Giles and Stuart, and Stuart then topping up by taking in Port Pirie.

In terms of how I calculated the margins, the methodology is similar to how I’ve done all my recent state and local redistributions. When it came to the two-candidate-preferred figures I ignored any SA Best results, since I don’t expect them to be the same party in 2022. This left just three seats where an independent made the top two. The independent seat of Mount Gambier underwent no changes at all, but the changes in Florey and and in Frome/Stuart were dramatic.

I have assigned Stuart as an independent-held seat. Just over half of its population came from the independent-held seat of Frome, where Geoff Brock polled 75.4% of the two-candidate-preferred vote. The Liberal Party polled 53% of the two-party-preferred vote in the Frome half of Stuart, and 72% in the other half. So I have estimated Brock’s two-candidate-preferred vote in the Stuart half of the seat at a bare 56.2%, which adds up to a margin of 16.1%. I have flipped Frome from independent to Liberal, so the overall seat count does not change.

I used a similar methodology in Florey, but the areas are less different to each other and independent MP Frances Bedford does not have such a large margin. Just 53.5% of the new seat of Florey was already in Florey in 2018, and Bedford polled 50.8% in that area. Bedford’s main opposition was Labor, who did 2% better in the other half of the seat, so I gave Bedford 52% in that area, for an overall margin of 1.7%.

Unfortunately for Bedford, the remainder of the seat was split into three parts, and she generally did better in those parts. So it’s conceivable she could decide to run instead in Newland, which gained suburbs where she polled close to 70% of the two-candidate-preferred vote, but only 14% of the new Newland was previously in Florey.

The biggest margin changes, apart from Frome, Florey and Stuart, were in Hurtle Vale (+3% for ALP), Playford (+2.7% for ALP), Reynell (+5.2% for LIB) and Hammond (+2.8% for ALP).

A uniform swing of 0.7% would see the Liberal Party lose their slim majority, while a uniform swing of 6.1% would give Labor a majority. The swing for the Liberal Party to lose was 1.0% prior to the redistribution, but Labor’s swing-to-win figure has not changed. Overall this creates an open window for a hung parliament if Labor gains a handful of seats.

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