This is a subject I've talked about before at some length, but I always like to revisit it. Namely that maps, especially those drawn before the 17th century, have been more representative and ideological than realistic with proper distances mapped upon them. Indeed I cannot think, off the top of my head, of any map that was used as a navigational tool prior to the 17th century. Most of them were in fact ways of demonstrating sacred geography (the T-circle map with Jerusalem at the center, for example). Not being well-schooled in medieval navigation, this begs the question of how ships found their way to where they were going without a good, accurate, vision of what the shores looked like, how pilgrims managed to get successfully from one city to another, and things of that nature. I don't know the answer to that yet, though I intend to start investigating it now that the idea has come into my head.
More importantly for this discussion, maps that players look at don't really have to be accurate. I've been brutally murdering myself for years over how to produce a series of accurate maps that remain accurate at all levels. This has driven me to make files with massive resolutions, to add minute details, generally to go crazy. I've made worldmaps, hexmaps, regional maps, town maps. I've crashed computers with the files I've asked them to handle so I could be sure that when I zoomed in, features wouldn't change places.
And yet, and yet—the maps available to a PC and the mental image they would have of their world... are probably not even half as good as the maps I've been struggling to produce. On the other hand, we are dealing with a fictional world that we're asking other people to inhabit with their minds. There is a reason that many fantasy novels begin with one important thing, before there is even a story on the page, and that is a map. How difficult is it to place oneself beside oneself and into a new, nonextant, land, to hold the notion of an unreal place within themselves and convince themselves that they can see it? VERY. So maps serve a useful and important purpose. To relegate them merely to the status of cultural relics wherein players cannot be certain of the actual shape of the world (or, more accurately, players can only understand the world as their characters do, requiring yet another level of commitment on top of what is already a staggering amount of mindwork we ask them to do) is a dangerous question for those who wouldn't breach the verisimilitude and play environment. What, then, are we to do?
Clearly the maps must have some utility, as well as appeal, for them to work. But they do not need to have the utmost utility. They can be wrong in places, or the scale can be off without causing a player meltdown. More importantly, there are many things that would not show up on these maps of theirs. Certain ruins, for instance. Bandit camps, hidden dwarven holds, and all manner of goblin and orcish settlements. Which is not to say they cannot add them to the map as they go, a time-honored tradition of marking the conquests of a party.
Maps are something we must treat with care, lest we on the one hand drive ourselves (as I have) insane with trying to keep them as accurate as possible or on the other make it impossible for players to understand the layout of their world.