I believe aping Tolkien (both directly, and indirectly through other authors that aped him) is the biggest reason behind this convention. Fantasy literature in general has been incredibly genre-conforming, though it would seem to be getting less so lately. Maps are just another element that's been subject to this sticking to familiar ways.

Quote Originally Posted by ravells View Post
I'm sure you're right Daelin...almost by definition Fantasy worlds depend on 'the unknown' or 'here be dragons' bits of the map to echo that idea that there are new frontiers to be explored. I think it was Umberto Eco who said that at it's heart, every novel is a detective novel, in that there is a mystery which needs to be solved. In the case of Fantasy, I guess the mystery is often geographical.
I disagree with this. What lies outside the bounds of a map rarely has ANY relevance whatsoever to the plot of a story. Fantasy authors, when they bother to dabble in cartography at all, probably choose to present a less-than-global picture of their world because
a.) they only NEED to show a small fraction of it and anything more might just confuse the readers,
b.) they're being lazy gits that can't be arsed to draw more than what's necessary,
c.) they actualy don't have a detailed idea about the world outside the confines of the story anyway,
d.) representing a smaller area on a given stretch of paper (usually a single page) = more space for details,
e.) any/all of the above.

If there is a conscious decision to include mystery, it's more likely to be worked within the plot than on a piece of supporting art. And should the latter be the case anyway, it's more likely to be flat out marked on the map (ie. by "Terra Incognita" labels or similar ways) instead of expecting the reader to get all excited about there being an edge to the map