Whenever any improvement district is created, the cost of improvements, or the portion thereof to be defrayed by special assessments, shall be assessed against the tracts or parcels of land included within the improvement district specially benefited thereby, but not including any tract owned by the United States of America or any agency, instrumentality or corporation thereof, or any streets or public highways. Such special assessments may be apportioned on any equitable basis, as may be determined by the council. (Ord. 9, Series 1988)