In any district, the owner of a tract of land comprising not less than 3 acres may submit to the Planning and Zoning Commission a plan for the use and development of all of such tract for uses permitted in such district, or for any uses permitted in any other district allowed hereunder if an underlying zoning district change to such other district is also requested, the procedures stated in Chapter 1109, Zoning Code Amendments, shall be followed. A development of land of less than 3 acres may be accepted by the Planning and Zoning Commission if such land is found to be suitable for a Planned Unit Development by virtue of its unique historical character, topography or other natural features, or by virtue of its qualifying as an isolated problem area.