As the caption accompanying this image indicates, this is a revised floor-plan for the first floor of the Mackay mansion, made for the publication of Mckim, Mead & White's monograph, in 1915.
The caption accompanying this image reads as follows:
Misleadingly the date "1902", does not refer to the disposition of Harbor Hill, but only to the time it was deemed "complete." The cause of tremendous confusion, this is a revised floor-plan, made for the publication of Mckim, Mead & White's monograph, in 1915. The large room in the south-west pavilion, with three windows, on both the south and the west, was, from 1902, to about 1905, the library, Harbor Hill's French oak paneled-principal living room. Transformation of this space into the "stone room", a salon that served exclusively as a space for entertaining, required that the billiard room, be made into a new, more intimate library. By 1925, thanks to Joseph Duveen finding a nearly complete French gothic room, the new library was redone, a third time and rechristened, the "gothic room". Twenty years earlier, the billiard room had been relocated, in the casino.
See Harbor Hill, Clarence Hungerford Mackay's Mansion.