100. Each company shall maintain on file with the Commission a map of each of its exchange service areas. Such maps shall show the exchange service area boundaries in sufficient detail that they ma y be located in the field. Such maps shall show the company's existing lines and facilities outside the base rate area and, its lines or extensions thereof under construction, and such maps shall be supplemented or amended from time to time by the filing of work orders or other construction, so as to enable the Commission to have reasonable complete information as to the general location of the existing facilities of the telephone company within an exchange service area or a portion thereof but outside the initial or base rate area. In lieu of complying with the provisions of Rule 12, telephone companies may supply work orders, or other documents for rural extensions of over one mile in length if within 60 days of the end of each calendar year they supply a system map showing all extensions made.