Base.wz

Base.wz contains references to all of the other WZ files as subdirectories. It also contains StandardPDD.img (used in defense calculation), and various z-order mapping and sprite-order mapping files for references used in drawing characters and maps.

So, in really low terms, its like a phone book for all/most things used in game that is visual and a few others, which the game engine itself uses when collecting the data from the other WZ files? a-@