Yes, there is one unexplored corner on my current world since the track actually diverts inward from the world edge here and there for variety, since something like 90% of the landforms are tundra with medium-to-large lakes--Very few spots actually get rain, and I've witnessed 'thundersnow' more than once .
I know I've had to re-craft maps from time to time after getting killed while holding them and not making it back to the death-spot before the dropped items de-spawned (I had read it was 5 min, but timed it once and saw them vanish after three), but I could have sworn I had to re-explore the world after replacing a de-spawned map item.
---PCJ
It's not really what's filled in on the paper maps in the game; but what chunks the system has saved to the file. For example, if you have 2 players in your world, your map only shows the areas in that world where you have been; not where the other player has been; but the system will have generated the chunks around both players and saved those to the world save file. After it generates the chunks, it no longer accesses the terrain generation formula to re-render the terrain; but accesses the saved file (which is where it also ultimately saves any changes the players make to those saved chunks, regardless of whether both players or only one have that area filled in on their paper maps. Regenerating a new map does not ungenerate the terrain itself. If it did, any changes you've made to the terrain would also disappear whenever you generated a new paper map in the game.
It's not really what's filled in on the paper maps in the game; but what chunks the system has saved to the file. For example, if you have 2 players in your world, your map only shows the areas in that world where you have been; not where the other player has been; but the system will have generated the chunks around both players and saved those to the world save file. After it generates the chunks, it no longer accesses the terrain generation formula to re-render the terrain; but accesses the saved file (which is where it also ultimately saves any changes the players make to those saved chunks, regardless of whether both players or only one have that area filled in on their paper maps. Regenerating a new map does not ungenerate the terrain itself. If it did, any changes you've made to the terrain would also disappear whenever you generated a new paper map in the game.