Each zone has its own subfolder. The folders are named with the Zone ID.
Each zone subfolder contains a list of text files titled in a x000y000.txt format. These files contain a list of props. Refer to Scenery File Format.
The X and Y coordinates of a particular tile are derived from the zone's page size. Typically 1000 game units (most official zones) or 1920 (actual terrain tile size). Refer to the ZoneDef PageSize property to get the actual page size.