Adoption of the plan or of any part, amendment, extension or addition shall be by resolution of the planning commission, carried by the affirmative votes of at least a majority of the entire membership. The resolution shall refer expressly to maps and other descriptive matter intended by the planning commission to form the whole or part of the plan and the action taken shall be recorded in its official minutes of the planning commission by the identifying signature of the chairman and secretary of the commission. A copy of the plan or part thereof as adopted shall be certified to the appropriate governing authorities and to all other legislative and administrative agencies affected by the plan.