Any municipality may exercise the powers granted under the provisions of this chapter in the total area within its corporate limits upon passage of an appropriate ordinance to that effect by the governing authority. Any county may exercise the powers granted under the provisions of this chapter in the total unincorporated area or parts thereof upon the passage of an appropriate resolution to that effect by the governing authority. Unincorporated areas adjacent to incorporated municipalities may be added to and included in the area under municipal jurisdiction for the purposes of this chapter provided that the governing authorities of the municipality and county involved shall agree as to the boundaries of such additional areas described in terms of easily identifiable physical features and landmarks and established political entities, procedures for the exercise of powers granted in this chapter and the manner of obtaining equitable representation on the boards and commissions provided for under this chapter. The agreement shall be formally stated in appropriate official action by the governing authorities involved.

The governing body of any municipality may designate its county planning commission as the official planning commission of such municipality. In the event of such designation, and acceptance by the county planning commission and the governing authority of the county, the county planning commission may exercise such powers and duties as provided in this chapter for municipal planning commissions as are specified in the agreement reached by the governing authorities. Such agreement shall specify the procedures for the exercise of powers granted in this chapter and shall provide for the equitable representation of the municipality and the county on the boards and commissions required by this chapter. This agreement shall be formally stated in appropriate official action by the governing authorities involved.