The applicant for approval hereunder of a plan of subdivision of a tract or parcel of land, the subdivision area of which exceeds 50 acres, may elect to apply for approval of the subdivision of a portion of the subdivision area. Such election shall be made in writing by filing with the application hereunder a written statement describing the proposed stages of development in detail and by showing, clearly and distinctively, on the accompanying record subdivision map and site development plan the areas to be included in each stage of development, designating and delineating the portion for which approval is sought as "Section I" and the other sections consecutively designated by Roman numeral in the order of proposed development thereafter. The entire road in all stages of the subdivision area shall be shown on the record subdivision map. In the event that subdivision approval is granted hereunder, such approval shall relate to, and authorize subdivision of, only the plan area designated and delineated for immediate approval as "Section I." The portion of the subdivision area designated for subsequent development shall, nevertheless, be considered a part of, and considered shown on a map of, an approved subdivision for purposes of the definition of the term "resubdivision" hereunder.