The gold value listed on the region page is not the tax income. It is, essentially, the economy value of the region, measured in gold per day. A gold rating of 1,600 means that, each day, there are essentially 1,600 gold coins of business transactions that you can tax, assuming a 100% production level. To figure out the actual taxes generated per day, you need to apply your tax rate to that value, then multiply by the production value. Like this:
GoldValue * TaxRate * ProductionValue = DailyTaxIncome
Multiply that by 7, and you get the weekly tax income generated by the region during one normal tax week.
