Within the Special District, any zoning lot existing on September 11, 1975, may be subdivided into two or more zoning lots provided that the existing topography, all individual trees of six inch caliper or more and all land located within a designated open space, to the greatest extent possible, are preserved under future development options. Any subdivision that is proposed to take place within the Special District after September 11, 1975, shall be filed with the City Planning Commission, and the Commission shall certify that such subdivision complies with the approved South Richmond Plan and the above objective. In the case of a subdivision of a tract of land containing designated open space, a site plan indicating the distribution of bulk for the individual zoning lots shall be submitted to the Commission. Such approved subdivision shall then be recorded in the land records and indexed against all zoning lots. The subdivision plan shall include a survey map indicating existing topography at two foot contour intervals, all individual trees of six inch caliper or more, and the location of designated open space within the area. When a zoning lot existing on September 11, 1975, is more than five acres and is intended to be subdivided, an area plan of the entire subdivision shall be filed with the Commission. The area plan shall include the proposed vehicular circulation system within the area, block and lot layouts and any other information required by the Commission.