It shall be the intent of this zoning district to encourage the best possible site plans and building arrangements under a plan of development rather than under lot-by-lot regulations. The developer benefits from better land utilization, economy in the provision of roads and utilities and flexibility in design. The city gains the advantage of a variety in building types, compatibility of use and optimum community development. The planned residential development is intended to encourage ingenuity and resourcefulness in land planning including a variety of housing types in a mixed use environment of residential and commercial services, to assure the provision of open space such as parks and recreational land and other facilities for the use of the occupants of the development, to provide for a more efficient and imaginative development of property and to facilitate efficient housing.