I'm surprised this conversation hasn't been had yet! Should rivers be mapped along hex edges, or as full hexes themselves?
"As full hexes themselves"? Like, visually?
I've always preferred "inside the hex", and declaring that hex a "river' hex for whatever ancillary effects I'm invoking at any given time. On the edge, at least for the 6 mile scale, feels like it gives too much game effect to the river; though for 1.5m hexes I'd wager that'd be not as important.
It's always been my feeling that, with six mile hexes, your hexes are too large to have the full hex be a river. I define a 'river' hex as 'a hex that contains a sufficient amount of river'.
The widest rivers in the world, at their widest points, are more than six miles wide. But the vast majority of rivers are not.
With 1.5 mile hexes, it's a different story, and a river that's close enough to taking up the entire hex (maybe three quarters of a mile wide) are a lot more common.
I draw my rivers freely, there's too much need to branch and switchback to stick to hexes, at least at the 6mi scale as others have pointed out.
I tend to only employ the "river" tables from the book if players are moving on a vessel on a river, and therefore benefiting from the increased movement speed.
Interesting! I guess I'm the only one OCD about this. My personal hangup with hexes bisected by rivers is that I feel like fording the river should be an event with some kind of meaning, but that makes it a hex with two halves, which is awkward because it goes against the whole aesthetic of hexes-as-smallest-meaningful-unit-of-movement. It'd be like cutting a tile in half in checkers.
Hexes (or squares) arent really a hard and fast thing on terrain. We use them specifically for convinence.
Even a fast flowing stream (river, creek or even irrigation channel) only a few metres across (or deep) can cause issues for fording. Liekwise even if on the edges of hexes large rivers will encorach a lot into the hexes it adjoins.
To me it sounds like for the way you want the rivers to behave/represent, mapping them along the edges of hexes will be your best solution as that will mostly prevent the bisected hex issue.
I suspect why there isn't really any codified way to handle rivers and the like, as what works best from group to group varies so much.