The re-election prospects of the first term Marshall Liberal Government have been dealt a major blow, after it was defeated on a bill in Parliament.

No, it's not contentious land tax changes, which have caused all sorts of pain for Premier Steven Marshall.

Rather, Labor and crossbenchers in the state's Upper House teamed up to defeat a change to the state's constitution, which would have reinstated a so-called "fairness clause".

South Australians are still more than two years from going to the polls to pass judgement on Mr Marshall's first term, but the field of play is already being set.

Not by voters, nor political parties, but by three people sitting around a table drawing lines on a map.

Honourable Justice Trish Kelly is one of three people examining the borders of seats in State Parliament. ( ABC News )

The Electoral Districts Boundaries Commission of SA is starting to examine the borders of seats in State Parliament, and if history is anything to go by, its final decision will have a major impact on who will be in the top job at the end of March 2022.

The Electoral Commissioner Mick Sherry, the Surveyor-General Michael Burdett and the Honourable Justice Trish Kelly will spend the next year coming to grips with new seat boundary rules they need to follow.

It is an independent body, following rules set by the state's politicians, who often have nakedly political motivations.

Until now, the commission has had to contend with the "fairness clause", a rule designed to ensure the party that wins the most votes goes on to win the most seats.

No other state or territory has anything like it, and previous boundaries commissions have struggled with putting its lofty goal into practice.

The commission radically redrew boundaries to satisfy the clause before last year's election, shunting several Labor-held seats into Liberal territory.

One third of voters found themselves in new seats, and the commission met the requirements of the fairness clause by allowing the population of some seats to vary by as much as 10 per cent from the average.

That helped Steven Marshall win the election, despite the fact that the Liberal Party actually went significantly backwards on first preference votes.

Labor was outraged at the redistribution, which meant that the vote of someone in the electorate of Flinders was worth 25 per cent more than the vote of someone in Elizabeth.

'Fairness clause' resurrection rejected

The former government scrapped the fairness clause on the last sitting day of the former parliament, and the Liberal Party has been trying to bring it back.

Following yesterday's vote, it seems the fairness clause will be consigned to the dustbin.

That means another major redraw of seat boundaries is on the cards.

Without needing to contort seats to satisfy the rules, there is less reason for the population of seats to vary as much as they currently do.

Premier Steven Marshall and Attorney-General Vickie Chapman. ( ABC News: Nick Harmsen )

That's a point we can expect to see the ALP argue forcefully.

Labor will likely ask the commission to in effect roll back some of the changes made before the last election.

In other words, to produce an electoral map more favourable to Labor.

The party will argue the most important principle to follow is that each person's vote should have the same value.

There are other factors influencing seat borders, including that "communities of interest" are reflected in State Parliament, and that seats are of sensible shapes.

Whatever decision is made about seat boundaries, the deliberations of those three independent public servants will have a major impact on the campaign we see in 2022.