Let me give you an example how to *not* do it...
WotC's Forgotten Realms Campaign Guide and Players Guide.. for 4th ed.
All the setting info, region descriptions.. what little there is... virtually identical.
Only reason both sold at all is, campaign guide came out right behind the core books, the players guide like 2 or 3 months after.
100% agree here.
I think boxed sets are the way to go, like old school D&D.
Each should have a players 'gazetteer' with a brief history and geography lesson, details of current political/racial tensions, and a Chapter or two on specific changes to the CRB regarding PC generation, magic and whatever is important for PLAYERS to know.
A GM book with more detailed info on the stuff in the players book, hooks, plots stat blocks of prominent NPC's whether they be potential allies, enemies or patrons. A bestiary can be included if space permits or that could be a 3rd book. Put all that together with some nice poster and reference maps in a box and viola! A complete setting.
If you don't want to do a boxed set, do each in the Legend format but dress it up a bit - more like Pinnacles Savage Worlds and release them individually in print and PDF. The GM book should come with the maps in a format that can be used in a variety of ways.
Glory is the reward of valour.
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