Accomplish, by the use of permitted flexibility and variation in design, a planned development that is as good or better than that resulting from the traditional lot-by-lot development, with total net improvement to be gained by combinations and options of: placement, type and bulk of building structures, coordinated open space, recreation facilities, other public facilities, such as walkways, controlled circulation, conservation of natural features, decreased water and air pollution, aesthetic features, harmonious design and similar elements;