Whenever a parking area is located in or adjacent to a residential district it shall be effectively screened on all sides which adjoin or face any property used for residential purposes, by an acceptably designed fence, or planting screen. Such fence or planting screen shall be not less than four (4) feet nor more than six (6) feet in height and shall be maintained in good condition. In the event that terrain or other natural features are such that the erection of such a fence or planting screen will not serve the intended purpose, then no fence or planting screen and/or landscaping shall be required.