My customary approach to maps -- be they outdoor or indoor -- is that they are kept hidden from the players until they have been fully explored.*
I assume this is the conventional way of going about things. The reasoning being that players will naturally use the map to direct their characters from a god-like aerial vantage point -- an advantage that would skew the first-person structure of roleplay to the game's detriment.
While this is an entirely possible scenario given the options normally available to characters in most versions of the D&D, I think there is a way that we can keep the map completely visible on the table AND use the player-to-character knowledge gap to one's Referential advantage.
By "gap" I mean the fundamental difference between what the player knows as he's playing the game and what the character he's directing knows. With a map laid out before his eyes, the player knows the general lay of the land and can foresee the consequences of movement in any direction. Unless the character was very familiar with his surroundings, his perception of his environment would be much more limited and short-range.
With full knowledge of the map, however, the player-character would be immune to misdirection, incapable of being lost...
But what if that wasn't always the case? Without a compass or a clear view of the sun -- say under a forest canopy -- there's a chance that any of us could be lost in the woods. What if those woods are not entirely natural? Perhaps the trees hide an invisible intersection of Ley energy-lines, giving them a subtle but pervasive phantasmagoric aspect that wreaked havoc on one's sense of direction...
Every two turns that they travel through unfamiliar/unknown territory, the party must check to see if they have become lost. The lead PC/NPC makes a WIS check using 3d6, subtracting his Experience Level from the result of the roll.
- Dense foliage or Low visibility (+6)
- Under the effect of Panic or Fear (+6)
- Exhausted (+3)
- In pain or Wounded (+3)
- Quasi-magical/Magical environment (+1 to +12)
Failure of this check indicates that the party has become bewildered.
A bewildered character has a 1-in-3 chance of "defying" player direction. This situation applies specifically to (1) large-scale overland travel and (2) dungeon navigation. The player must state his intention (eg, "Brown Dweezel takes the left passage") and then the Referee checks to see if the character will botch the player's plans. Failure here indicates that the character moves in a different, random direction. THUS "Instead of taking that left turn, Dweezel continues forward a full move." Things will continue in this fashion until the character has followed player direction successfully three times in a row.
*In most cases, there will be a "player version" of the map -- a version that omits most secret or hidden items and locations.