Not less than 2% of the above required 10% of the total gross acreage of a lot with residential use shall be designated as and devoted to usable open space, subject to §§
365-90 and 365-99 and Article
XXXI, in the form of pedestrian gathering areas, such as parklets in the range of 400 to 500 square feet, courtyards in the range of 500 to 2,000 square feet, plazas in the range of 2,000 to 3,000 square feet, and other pedestrian gathering areas of 3,000 square feet or more, that are located in close proximity to buildings in the R-3A District.