Where land lying partly within the boundaries of the City and partly without such boundaries of the City are transferred, the tax herein imposed shall be calculated upon such portion of the value as shall be represented by the portion of such lands lying within the boundaries of the City, such apportionment of value to be evidenced by the affidavit or certificate of value hereinafter provided for, but shall in no event be less than the highest assessed valuation for local tax purposes, placed upon the same in the assessment of property within the City.