Section 26. There is hereby established a metropolitan area planning district, in this section and sections twenty-seven to twenty-nine, inclusive, called the district, consisting of the following cities and towns:—

and any other city which by vote of its city council and any other town which by vote of a town meeting applies to the council to be included in the district and whose application is approved by a majority vote of the council; provided, that any such city or town is within an area which is being urbanized and which adjoins the metropolitan area planning district and has common or related urban planning problems.

The district shall constitute a public body politic and corporate and, if designated by the Secretary of Commerce of the United States, shall be an economic development district in accordance with the provisions of the Public Works and Economic Development Act of 1965.