How does one rate work?

I could answer, I have no idea.
Most councils calculate the rates on cents in the dollar on the Valuer General's valuation of a property. The number of cents is calculated so that the final amount is the amount of money that is needed to manage the council for the next 12 months. So the more valuable your property the more you pay. But it is also true that the more expensive the houses the lower the rate in the dollar. So if you live in Salisbury and have a $500,000 house you would be paying much more than on the same amount on Unley. How then does one rate work? If a uniform rate in the dollar was charged across the entire city the Unley residents would be paying much higher rates. I don't think any residents would be very happy with this outcome. So how does it work? I still have no idea but is someone wants to let me know feel free to comment.