Here's how it's done in Ontario where I live:
1. Assessed value ≠ market value. Assessed value is determined by some criteria such that sqft, #rooms, desirability of neighbourhood, pools, etc correlate with the final value.
2. Actual value doesn't matter at all. If everyone's assessed values go up 10% in the municipality, property tax bills change by $0. What matters is the relative assessed values. They determine how much of a city's tax bill the household pays.
3. The actual process for determining the tax bill: city comes up with a total figure to be collected. City sums all assessed values of all properties. Divide former by latter to get a multiplier (e.g. 1.355%). That multiplier times assessed value is your property tax. (It's a bit more complicated because they collect slightly different amounts from different property types).
Is it different in California?