As a condition of approval of a tentative parcel or subdivision map, there may be imposed a requirement that improvements installed by the subdivider for the benefit of the subdivision contain supplemental size, capacity, number or length for the benefit of property not within the subdivision and that those improvements be dedicated to the public. However, when such supplemental size, capacity, number or length is solely for the benefit of property not within the subdivision, the county shall, subject to the provisions of Cal. Gov’t. Code §§ 66486 and 66487 of the Subdivision Map Act, enter into an agreement with the subdivider to reimburse the subdivider for that portion of the cost of such improvements equal to the difference between the amount it would have cost the subdivider to install such improvements to serve the subdivision only and the actual cost of such improvements. (Formerly 23.20.001)