The district as formed may include unincorporated or incorporated and contiguous unincorporated territory. The incorporated territory included in the district may include the whole or part of one or more cities. However, the whole or part of a city shall not be included in a district except by the vote of a majority of the governing board of the city. The district shall not include the whole or any part of any other district formed for similar purposes unless the governing body of such other district shall consent thereto and the board of supervisors shall find and determine by resolution duly adopted that the proposed inclusion of the whole or part of such other district is in the best public interest and the territory affected will be benefited thereby.