In this thread since this contains Dawnguard spoilers.

Since the release of the game, i used to think the Skyrim map was just a model made to look like an overview of Skyrim, with clouds moving and the sky changing colour based on the time of day to make it look more realistic. But just then i summon Durnehviir and as he burnt up into a purple flame i used the Map, and i could see the purple flame and its purple flame trail in the sky, where he was flying... now obviously time doesn't pass, so it was still, but it was quite odd.

It makes me wonder how the map render works?

The map is made in realtime, more or less. Next time you absorb a dragon's soul, go to the map while the soul capture is in progress. There should be a bright spot where you're located at.

This comes with the additional benefit of not needing to make a new map for each DLC the release, unlike with Oblivion and FO3/NV.

I'm pretty sure it was real-time in vanilla too

Wow that's something new.
However , I use the physical map.