No such regulation, restriction, or boundary shall become effective until after a public hearing in relation thereto, at which parties in interest and citizens shall have an opportunity to be heard. Notice of the time and place of such hearings, as well as the location of the affected districts, by naming townships and sections and, if possible, by describing the roads and streets that form the boundaries of the affected area, shall be given by publication thereof in a paper of general circulation in the City at least one time, not less than four days or more than 20 days prior to such hearing.