Any tract of land, hereinafter known as the "development tract," proposed to be developed shall be in single and separate ownership or, in the case of multiple tracts and separate ownership proposed to be combined for such development, at the time the application is filed with the Board, there shall be submitted therewith a written agreement in the form of a declaration of restrictions, covenants and easements, in a form suitable for recordation, which imposes upon all such tracts the condition that they be developed in accordance with a single plan, with common authority and common responsibility, so that the tracts so combined are developed as a single development tract in accordance with the zoning regulations of this district and the subdivision and land development regulations established in Chapter 72 of this Code.