Density. A cluster development shall result in a permitted number of building lots or dwelling units which shall in no case exceed the number which could be permitted, in the Planning Board's judgment, if the land were subdivided in lots conforming to the minimum lot size and density requirements of the zoning district or districts in which such land is situated and conforming to all other applicable requirements. For this purpose, the applicant/owner shall submit a sketch plan for a conventional subdivision to establish the maximum possible number of units and the Planning Board may require any additional information it deems necessary to make this determination. Where the subject tract of land falls within two or more contiguous zoning districts, the Planning Board may approve a cluster development representing the cumulative density, as derived from the summation of all units allowed in all such districts, and may authorize actual construction to take place in all or any portion of one or more of such districts.