Section 403.375 - Boundaries of zones(1) The board shall adjust zones established within a district as necessary to make them as nearly equal in population as is feasible according to the latest federal census. The board also shall adjust boundaries of zones as necessary to reflect boundary changes of the district.(2) For purposes of ad valorem taxation, a boundary change must be filed in final approved form with the county assessor and the Department of Revenue as provided in ORS 308.225.