I've never seen the map zoom in skyrim in action, but from the look I would guess, that they use some kind of LOD for the terrain mesh and texture.
They do exactly that.
Even before Skyrim, Bethesda had their whole world map rendered into different levels of detail, stored into meshes and textures inside the game files. The LOD system picks up the different levels it needs and loads the models accordingly. So nothing is processed real time in that respect, its just pre-made low poly/low res models/textures loaded as the game needs them.
For Skyrim they just picked up the least detailed level and assembled it into a 3D map. Make terrain LOD, get a sweet and free ingame map. Pretty clever
@riuthamus. I guess that if you want exactly the same on a voxel world, you'd need to generate the map on the fly, depending on what you're doing. If players can change the terrain, then it should be updated every time the player open ups the map. If it doesn't, you might get away with just generating it once on a "building world/loading game" screen before the game starts.
Or you could just set up intervals at a fixed time in which the map updates and just let the players wait for their stuff to appear on the map. Normal players aren't that picky with the technical details if the game keeps them entertained nevertheless.
As far as for the implementation, no idea, i'm not that experienced yet. All I know is what caldiar said, octrees could get you easily different interpretations of your world in different resolutions (more exactly, different cube sizes). By zooming in, you go into lower levels of the tree, by zooming out you go into upper levels. Though if you don't already have your map stored in a octree, changing the whole world representation may not worth the hassle.
I *think* that it may be too hard for the CPU to do all of that (massive traversing of octrees if the map is big enough), but I'm not sure, as I said, I don't have any relevant experience.
Edited by TheChubu, 27 September 2012 - 01:41 AM.