MoP
This page is for Mists Of Pandaria files only. Observations made in build 5.0.1.15464
ADT
These are separated into 5 files now (up from 4 in Cataclysm).
Map_X_Y.adt has terrain information.
Map_X_Y_obj0.adt has doodad and wmo information and the needed information in the MCNKs.
Map_X_Y_obj1.adt is new and also has doodad and wmo information and the needed information in the MCNKs.
Map_X_Y_tex0.adt and Map_X_Y_tex1.adt have texturing information.
Note : _obj0.adt and _obj1.adt don't have the same size
Otherwise, the structure seems to be the same as it was in Cataclysm.
WDT
MPHD chunk
Same structure. However, new WDT flags have been discovered.
Most of the new maps have "da" flags. Several of them have "5e" or "4e". Only one map (StormstoutBrewery) has "c8", and a few have "ca".
MAIN chunk
Structure hasn't changed. As it was the case in Cataclysm, 2 on a tile displays "fake water" ingame.
MWMO, MODF chunks
As there is no WMO-based map on the beta (every map has some ADT), I have not seen these chunks.