In the event an existing subdivision is resubdivided such that the street alignment, lot design or drainage shall be changed, then the area constitutes a new subdivision and the procedures for filing a tentative and final map as outlined in this chapter apply. The filing of the final map or parcel map shall constitute legal merging of the separate parcels into one parcel and the resubdivision of such parcel.
(`67 Code, § 11-7-2)