I've been revisiting the maps of Joan Blaeu lately (the wife got me a book of his maps awhile back). Scale bothers me on occasion, but I usually let it go. I've been paying more attention to small details lately though, and one of the things that really strikes me is the population density. The sheer number of towns and villages marked on the maps is incredible, compared to most fantasy maps. Plus one of the details I've noticed is something you bring up - walled cities and such on his maps actually get a basic layout, he draws in major streets and squares, plus walled outlines, which works at the scales used. Something I've been considering striving for in my own.
I think another thing to consider with setting density of towns/cities at a particular scale is the population itself. If it's based on historical europe, as so many fantasy worlds are, then is it a human only population, or are there other races and critters to consider?
Having lived in rural prairies, one thing I noticed is that during traveling there were towns every 15 mins or so along the major highways and roads (60mph or so so every 15 miles) .. which made sense - they were placed along the train tracks and at such a distance that a farmer with a wagon could get to town, exchange goods, and be home by sundown
Some of this might be seemingly random ramblings, but i *try* to keep things like that in mind, yes