The commission may adopt the plan as a whole by a single resolution or may by successive resolutions adopt successive parts of the plan, the parts corresponding with major geographical sections or divisions of the municipality or with functional subdivisions of the subject matter of the plan, and may adopt any amendment or extension thereof or addition thereto. Before the adoption of the plan or any such part, amendment, extension, or addition the commission shall hold at least one public hearing thereon, notice of the time and place of which shall be given by one publication in a newspaper of general circulation in the municipality and in the official gazette, if any, of the municipality. The adoption of the plan or of any part or amendment or extension or addition shall be by resolution of the commission carried by the affirmative votes of a majority of the commission. The resolution shall refer expressly to the maps and descriptive and other matter intended by the commission to form the whole or part of the plan, and the action taken shall be recorded on the map and plan and descriptive matter by the identifying signature of the chairman or secretary of the commission. An attested copy of the plan or part thereof shall be certified to the council.