I believe every hex should be potentially interesting.

But not all of the interesting stuff needs to be pre-planned. You can start with a 5 hex radius of the PC's starting location and then do more work as the PCs move in a particular direction.

Also, they don't need to encounter the interesting thing whenever they enter a new hex. Its possible that an "empty plain" could hide some impressive secrets that have to be discovered later in the campaign.

There is a Carcosa "alternate stuff" download that is worth looking at.

Quote from: noisms;477959On how many hexes do you usually pre-plan something of interest (meaning an encounter, named settlement, dungeon, lair, etc., not just geographical features)?

I put at least one keyed encounter in every hex, but use a system where any given expedition through a hex is unlikely to trigger the keyed encounter. This, combined with random encounters, means that the players never feel like they've "cleared out" a given area.

I think a lot of it depends on the size of the hexes. I try to detail enough hexes so if the PCs ride for a day or two, they're more likely to bump into a keyed encounter than not. I use 3-mile hexes, so 1 in 10 is my rule of thumb. If I were using 6 mile hexes, I might try to bump it up a little more, maybe into the 15-20% range.

These days, just to make it easy for setup, I go with about 20 detailed hexes or areas for any given map or area. Any more is wasting time detailing the game world when it may not get played, and any less risks not having a enough prepared material for one single gaming session.

About 50% of the time, players head off into the unknown anyway, which is why I'm a big fan of having charts and generators handy at game time (Which I only use to go into detail on, if the players get off the beaten paths or storyline.)

Pathfinder's GM Mastery Guide contains notes on quickly generating minor Kingdoms and Provinces and is quite handy in this regard.

Also, outdoor random encounters and random encounter tables (I'm a big fan of these as well) means that any hex can potentially be or quickly become "Interesting".