A map - or any other image for that matter - can be made into a texture which can then be applied to a Placeable object. This Placeable can then be placed, hence the name, anywhere you like, in the game...
Here, for example, is a map I created for my Maldrapur Chronicles series, rendered as a Placeable which is stuck to a wall in Rajatnur Palace (from over on my PHoD Things thread...).
As Custom Content goes, this is a very easy thing to do... It's probably also the best way of rendering a world map in-game.
The Placeable can be any size you like and, if you don't want it on a wall, you can create it as a horizontal object so that it lies on the floor. You can thus have a floor map of your world covering several Tiles in an Area. If you wanted, you could then add little Placeables on top of the map to highlight cities and other features which could have scripts attached so that when manipulated, they teleport a player directly to that place... NWN is fairly versatile in that respect.
As to creating the Placeable Map itself, it really is very easy to do such a straightforward object. If you're not familiar with gmax and so forth, someone here will doubtless help you out. I'll happily splat the map texture (when you've got it finished, obviously,) onto a big blob for you if you advise what size, orientation, etc, you want...
