Under the standard provisions of this chapter, a separate ground area must be designated, provided and continuously maintained for each structure or use. Pursuant to the procedure hereinafter set forth, two or more such structures may be erected and maintained on the same lot. Also, several lots may be combined into one special plan covering a planned development group. The procedure is intended to permit diversification in the location of structures and to improve circulation facilities and other site qualities while ensuring adequate standards relating to public health, safety, welfare and convenience in the use and occupancy of buildings and facilities in planned groups.