The Player's Gazetteer is meant to be a pseudo-in-world document of BloodStone Isle. Certainly it is a collection of first-hand accounts, historical incidents, maps, and other lore and setting intricacies that will help the table become fully immersed in the tale you're telling.
 
The full book includes the following:
Maps of each region
Event timelines
Notes on regions and factions 
NPCs of import
In-world songs
Intricate riddles
The Spinster's Tale
Letters from the Baroness
Much, much more!