One of the important principles of democracy, alongside that of "one person, one vote" is that of "one vote, one value"
When the electoral boundaries for South Australia were drawn up in 1856, the designers of the Constitution believed that they should represent equal numbers of people as far as practicable, but that they should represent groups who shared similar geographic, economic, or class interests as well.
The main effect of this was that the electoral system gave extra political weight to voters who lived outside Adelaide. This was based on the belief that South Australia's economy was based on its rural producers, so they should have a greater say in the politics of the State. In 1932, rural over-representation was written into the Electoral Act, as part of the coalition agreement between the Liberal Union and the Country Party. This guaranteed that there would be two country seats for every city seat - so parties which had their main support in the cities had to get twice as many votes to gain government as their rivals with a base in the country.
This system continued until it was removed by a constitutional amendment in 1975. The principle of "one vote, one value" was then made the over-riding principle for electoral redistributions. This reform of the Constitution also made the Electoral Commission independent of Parliament and of politicians.