So I am working on an island for my home game, I don’t know how big I want it, but I do know that I don’t want it to be Australia big. My thought process behind this is that the characters find an old journal of some random adventurer or someone similar. There will be heaps of information inside of it like:
Maps (both of the whole island and random dungeons within the place)
Creature pictures and information (maybe weakness of some too)
Random berries and herbs (what they do, where they can be found)
Interesting locations (probably marked upon the island map, but have some information too)
Location of town or keep or whatever (depends how large the island is, and how “wild” it will be)
A bunch of random plot hooks.
So the main book will be some sort of handout to the players, where the rest of it will be for the GM. The GM section will have some sort of random tables for a bunch of different things to make the players doubt what was actually written inside of the book.
The main idea behind this is that player knowledge of the area is something that I think is good, it will also be used as an in game thing, so that when someone is looking though the book in combat that is their action.