Section 19. The directors shall submit said map and report to the board of aldermen of every city and to the selectmen of every town named in the agreement of association, who shall thereupon appoint a time and place for a hearing, of which notice shall be given by publication in a newspaper published in said city or town, or if none is published therein, in such newspaper published in the county where said city or town is situated as shall be designated by the department, at least once in each of two successive weeks, the last publication to be at least two days before the hearing; and by posting copies of said notice in two or more public places in said city or town at least two weeks before such hearing.