No subdivision shall be approved unless the area to be subdivided from an existing street on the Official Thoroughfare Map, such street is an existing state, county, city, or township highway, road or a street shown upon a plat approved by the Planning Commission and recorded in the County Recorder's office. Such street or highway must be suitably improved as required by these Regulations or guaranteed, with a performance bond, to be improved as required by these Regulations. In addition, no final plat of land within an existing zoning district shall be approved unless it conforms with requirements of the zoning district.