The state tax commissioner, at the time of certifying the equalized value of each organized county to the county auditor, shall certify the number of miles [kilometers] of each main line of railroad, and of the branch lines and sidetracks of railroad within the county, and the valuation per mile [1.61 kilometers] of the line and branch lines, if any, as determined by the state board of equalization, and the county auditor of the county shall apportion the valuation to the cities, townships, and districts through which the railroad and branch lines run according to the number of miles [kilometers] within the boundaries of each, as a part of the valuation of the city, township, or district for the purposes of taxation.