ORS § 199.765
The charter for a city-county shall specify the permanent rate limit for operating taxes for the city-county within the meaning of section 11 (3), Article XI of the Oregon Constitution. The permanent rate limit shall be a rate that would produce the same tax revenue as would have been cumulatively produced by the cities that are the subject of the consolidation, the county and all special districts automatically extinguished under ORS 222.510 or by ORS 199.705 to 199.795, not taking into account any applicable statutory rate limit on operating taxes. To provide for the administration of differential taxation, the charter may establish districts on the basis of services to be provided by the city-county and prescribe operating tax rates for the different districts, except that the operating tax rates may not cumulatively exceed the permanent rate limit established for the city-county under this section. The charter shall provide procedure for modification or dissolution of such districts and for changing such tax rate formula, after the first fiscal year in which the city-county imposes ad valorem property taxes.
ORS 199.765