The creation of lots of less area or frontage than that normally required for the zone district in which the lots are located may be permitted provided the subdivision design and arrangement of lots shall be in such a manner as to maintain the intended density of the zone district in which the modification is permitted. Further in order to permit the use of the additional open space area for the Borough for public purposes as outlined above, the title to open space which are created by virtue of the permitted reduction shall vest in the Borough.