A transportation district may be enlarged to include any additional county or part thereof, or city or part thereof, contiguous thereto, upon such terms and conditions, consistent with the provisions of this chapter, as may be agreed upon by the commission and such additional county or city and in conformance with the following procedures. The governing body of the county or city shall adopt an ordinance specifying the area to be enlarged, containing the finding specified in § 33.2-1903 and a statement that a contract or agreement between the county or city and the commission specifying the terms and conditions of admittance to the transportation district has been executed. The ordinance, to which shall be attached a certified copy of the contract, shall be filed with the Secretary of the Commonwealth. Upon certification by the Secretary of the Commonwealth to the Tax Commissioner, the commissioner, and the governing bodies of each of the component counties and cities that the ordinance required by this section has been filed and that its terms conform to the requirements of this section, the additional county or part thereof, or city or part thereof, upon the entry of such certification in the minutes of the proceedings of the governing body of such county or city, shall become a component government of the transportation district and part of the transportation district.