According to one comment in the Final Environmental Impact Statement
The DEIS states that the City's open-space goals are not considered impact thresholds, as it is understood that they are not feasible for most neighborhoods in New York City. Contrast this, though, with Battery Park City, which also has about a third of its acres set aside with parks and fields. When completely built it will have about 14,000 residents, so the ratio of open space per 1,000 residents meets the City's goal of 2.5 [acres].
The ESDC responded:
The percentage of open space in Battery Park City (approximately 33 percent) is comparable to the Atlantic Yards project site (approximately 36 percent—8 of the project site’s 22 acres). The proposed project would provide approximately 1.7 acres of open space per 1,000 residents on the project site. Although this number is less than the citywide goal of 2.5 acres per 1,000 residents, the citywide goal is not feasible and not achievable for many areas of the city and is not considered as an impact threshold for CEQR purposes.
That deserves a recalculation. For 8 acres of open space to represent 1.7 acres per 1000 residents, that would mean a project with some 4700 residents.
However, there would be 6430 housing units; at 2.4 people/unit, there would be 15,432 residents. At 2.1 people/unit (the FEIS estimate), there would be 13,503 people.
For a population of 13,503, a ratio of 1.7 acres per 1000 people would require 23 acres of open space--more than the entire AY project. For a population of 15,432 that ratio would mean more than 26 acres of open space.
For the smaller estimated population, there would be .6 acre of open space per 1000 people. For the larger estimate, there would be .5 acre of open space per 1000 people.