On or before October 31 each year, the department of revenue shall proceed to find the actual value of that part of such transmission line or lines referred to in section 437.2, owned or operated by any company, that is located within this state but outside cities, including the whole of such line or lines when all of such line or lines owned or operated by said company is located wholly outside of cities, taking into consideration the information obtained from the statements required by this chapter, and any further information obtainable, using the same as a means of determining the actual cash value of such transmission line or lines or part thereof, within this state, located outside of cities. The department shall then ascertain the value per mile of such transmission line or lines owned or operated by each company specified in section 437.2, by dividing the total value as above ascertained by the number of miles of line of such company within the state located outside of cities, and the result shall be deemed and held to be the actual value per mile of said transmission line or lines of each of said companies within the state located outside of cities.