Land, buildings, or premises in any district shall hereafter be used only for a purpose permitted in such a district and in accordance with the appropriate regulations. A permit of occupancy shall be issued by a qualified person designated by the city to the effect that the use, building, or premises conform to provisions of this and all related ordinances, regulations, and requirements prior to occupancy, for any building erected, enlarged or altered structurally for the occupancy or use of any land. Such a permit is needed whenever use or character of any building or land is to be changed.