Cartographic enlightenment

I've done a bit of research (i.e. surfing the net) lately on the subject of drawing maps for fantasy novels. I'm trying to create a convincing map for one of the worlds in which a couple of recent stories are set.

One thing which strikes me about almost all of the tutorials I've found is the manner in which they suggest writing your novel. The general consensus seems to be that the first step is to create the world in which the story is to be set. One or two of the tutorials even suggest mapmaking as a means to a plot.

What surprises me is the frequency at which this idea recurs. I'm not suggesting it's wrong, by any means - after all, it's a technique, and if it works for you then it's right. It is, though, a heck of a long way from how I go about writing stories, which got me wondering if perhaps I was alone in my methods. Let me try to explain how a story forms for me...

The first thing which happens is the imagining of a scene. This is always out of the blue, and never has to be considered. I usually let it brew for a bit before committing pen to paper or fingers to 'board. Into this scene I place a character. Typically, the character's, er... character, is defined by the scene in which they have been placed - it's always going to be perfectly natural for them to be there, otherwise the scene isn't going to gel. 

Once that scene is in place, I try to expand from it. What led up to this situation? What is a likely outcome? Is this the beginning of the novel (common), or the end (uncommon)? 

This leads to placement in a world. Often it's possible to shoehorn the scene/character into an existing world, but sometimes a new world is created. If the story progresses well, the new world will expand and evolve inside my head, until I decide that it's getting a little too difficult to remember all the names of the places where people have walked/ridden/stolen things/got killed. At that point, and not before, I draw out a map.

There's a good reason this is one of the last things I do - until the story is fixed in my mind, how am I meant to draw out a map of where everything takes place? It's a bit like the reason I don't come up with full plots before I begin writing - I don't know what happens to the characters, and even if I did write something down, things evolve so tortuously in my mind that it would bear no relation to the final product. If I drew a map before I started, it would look nothing like the world I ended up with.

I don't know; perhaps I am alone here. Perhaps it's more normal to plot and plan, and know what's coming before your characters do. I just can't work that way. It's not that I find it restrictive, it's just a waste of time because it's bound to be wrong. I'm much better just getting on with things and filling all that paperwork in after the event.

The map, by the way, is going rather well, although I am having a bit of an issue with deciduous trees...