DF handles it slightly different then us, because their “smallest” map chunks are significantly bigger (each one is about 48x48 IIRC, instead of like 16x16). Basically they just load up the 6x6ish chunk of “smallest” chunks and drop/reload them in memory, but I’m fairly certain that rather then doing a conveyor-belt style thing like we do they rather actually move the player around on the maps, only shifting them when they drop/reload sub maps. Biomes function fairly similarly, but DF biomes are separate on a z-level basis as well (it’s just that the underground ones are hidden on the map) thus allowing them to have varying biomes as you descend (technically there are only 5 underground biomes at the moment in DF, Cavern 1, 2, 3, Lava, and Hell).
