The county superintendent of highways of each county shall prepare a map showing a proposed county road system for such county to be constructed with moneys from the county road fund, such system not to include a state highway, except that a designated state highway not under state maintenance may be included in such system and be improved by a county. This map must be approved by the board of supervisors of such county before it becomes effective; and when so approved it shall be filed in the office of the county clerk and county superintendent. An existing map of a county road system, however, may be approved by the board of supervisors and, when approved by such superintendent, such action shall be deemed a compliance with this article, when the map is filed as above provided. Thereafter, except as otherwise provided by § 114 (Sources and use of county road fund moneys)section one hundred fourteen of this chapter, no road shall be constructed, reconstructed or maintained with any such county road fund moneys except the road set forth on such map, excepting, however, and notwithstanding any of the provisions of this article, any highway enumerated in § 341 (Designation of state highways)section three hundred forty-one of this chapter that has been constructed or improved under section one hundred and ninety-four or one hundred and ninety-five, or under the general or special law governing the construction or improvement of highways, that has been constructed or improved as a state highway, may be maintained from such county road fund moneys. Amendments to such map may from time to time be made by such county superintendent and if approved by such board of supervisors shall be filed in the office of the county clerk and county superintendent. Construction in accordance with such map shall, subject to the provisions of this chapter, proceed in such manner that any money in the county road fund used in any one year shall be used so far as is practicable to build or finish complete road units or projects as shown on such map within such year and not to construct parts of units or projects divided from each other.