Islaire is a planar location, the setting of “Memories of Amitlai”, a narrative of cosmological importance in the cycle. It is a center of inter-planar diplomacy, with the presence of factols (authorities of the outer planes) and embassies of devils, and a site of negotiation and political power in the multiverse.
It stands in contrast to the material geography of York, Torregrises and Tanastias: a center of abstract power and political negotiation in the outer planes.