Everything regarding maps is compressed, the map tile properties, the tilemaps and tilesets.
You could swap compressed tilesets by just swapping pointers:
Code:
D9A800 D9CD0F Map Tile Properties (42 items, compressed)
D9D1B0 DDFFFF Map Formations (350 items, compressed)
DE0000 DFB3FF Map Tile Formations (75 items, compressed)
You could swap compressed tilesets by just swapping pointers:
Code:
DFBA00 DFBAFF Pointers to Map Tile Formations (3 bytes each, +$DE0000)