Whenever the public necessity, convenience, general welfare, or good zoning practices require, the Mayor and Council may by ordinance, after recommendation by the Planning Commission and subject to the procedure set forth in this article, amend, supplement or change the regulations, district boundaries, or classifications of property now or hereafter established by this chapter or amendments thereof. Such amendment, supplement, or change may be initiated by resolution of the Mayor and Council, by motion of the Planning Commission, or by petition of any property owner.