In thinking about mapping, hexes, wilderness, overland travel, domain-level play, and so on, I've come across some really cool mapping resources I thought I'd share.
What's the Path? - Britain
If you play in a UK setting, you owe it to yourself to check this out. It's got a split-screen display between Google Maps satellite maps and detailed Ordnance Survey topographical maps and route planning that takes into account overland distance as well as ascent height, and applies Naismith's Rule to figure out how long it would take to hike the route.
It also will display the route in terms of ascent and descent in a cool little graph.
Vision of Britain Maps - Britain
This site has a bunch of nice topographical maps of Britain (and some of the Continent, as well), including a stunning version done in the 19th century. The 19th century hand-drawn version I found particularly useful for visualizing how big a hex is.
Look at the Lake District in England and mentally project a six-mile hex onto it. Look at all those hills, lakes, rivers, streams... It would take ages to explore that hex thoroughly. I realize that this is not a novel thought, but this map helped me understand this on a more visceral level.
While a more modern topo map has more hard info on it, something about the drawing style in this map gives me a better feel for the terrain.
Cassini Maps - France
Going back even further, these maps are from 1750-1790. If you haven't been to France, and traveled through the vast rolling hills of the south, covered in farmland, these could give you a good idea of just how dense the tiny communities are there - many of them dating back to the Medieval era, or before.
If you're running something that's similar to Medieval France, and you're not having the party come across a half-dozen little communities (<100 people) every day of travel, it's too sparse. Opening a random square of Southern France, there would be dozens and dozens and dozens of communities in a 6-mile hex. Even allowing for population growth between 1300 and 1750, there would still be many small communities around.