Agree with TC on all points. The world map is the purest distillation of the game's soul; a video game is as much a work of art as a book or a film, and everything they can do a video game can too. However, each medium does one thing better than others.
Books can take you inside a person's mind, and show you what a person thinks - things that plays and films can only suggest. Internal conflict is literature's métier.
Plays are auditory, and as such they display the parts of our lives defined by auditory input and output - communication and social conflict. A good play doesn't even need a stage. Why do you think radio plays were so popular before television?
Film, the primary medium of the last three quarters of a century, is primarily visual. It best explores external conflicts and physical violence, as opposed to social violence or internal emotional conflict.
There are so many types of games that any game can be more like a book, a play, or a film, at least in terms of conflict, though most games most resemble film. But the primary attraction of games - and the only thing they alone can offer - is to give the player the choice to experience the story as he wants to. This freedom is what the world map represents. As world maps became 3D and free-roaming, this sense of freedom expanded, and found it's most eloquent incarnation in the Final Fantasies of the Playstation One era. It is no coincidence that elimination of the world map coincided with an increase in the linearality of JRPGs.
World maps are not without problems. You cannot realistically represent the same world map from a player character and a vehicle point of view, which is why there should be different perspectives and (forgot the word) ratios for player characters and various vehicles.
The player character world map should be either a very small character roaming an truly enormous world map if you want to realistically represent the distances between places. That's if you want the bird's eye view. A less often seen POV is a slightly modified 3rd person or over the shoulder (with complete camera controls so you can look up and around as you move), with representations of forests and mountains towering over you, along with mists and clouds and flocks of birds and such. This is much more immersive, the former, though it can be easier to get lost if poorly implemented. For some, however, getting lost is part of the fun. ; )
Mounts or ground vehicles should have a similiar POV. Sea-based vehicles still another, and submersibles another. But my greatest annoyance is airborne vehicle POV in games like FF7... You lose so much of the charm of the world when your vehicle is the size of a town, and when it takes you 30 seconds to circumnavigate the globe. I don't know how to fix it without defeating the purpose of the airborne vehicle (ease and speed of movement), but it's still better than no world map.