The Council shall have the power to determine the necessity of any local or public improvement and to determine that the whole or any part of the expense thereof shall be defrayed by special assessment upon the property especially benefited and shall so declare by resolution, provided that all special assessments levied shall be based upon or be in proportion to the benefits derived or to be derived. Such resolution shall state the estimated cost of the improvement, what proportion of the cost thereof shall be paid by special assessment and what part, if any, shall be a general obligation of the City, and the number of installments in which assessments may be paid, and shall designate the districts or land and premises upon which special assessments shall be levied.