NML:List of tile classes
From GRFSpecs
Vehicles, Stations, Canals, Bridges, Towns, Houses, Industries (Tiles), Cargos, Airports+Tiles, Objects, Railtypes, Roadtypes, Tramtypes, Roadstops, Terrain
| TILE_CLASS_GROUND | Clear ground and farmland | 
| TILE_CLASS_RAIL | Rail and rail depots | 
| TILE_CLASS_ROAD | Road, road depots and level crossings | 
| TILE_CLASS_HOUSE | Houses | 
| TILE_CLASS_TREES | Clear tile with trees | 
| TILE_CLASS_STATION | Station, waypoint, station part of oilrig | 
| TILE_CLASS_WATER | Sea, canal, ship depot | 
| TILE_CLASS_INDUSTRY | Industry tile | 
| TILE_CLASS_TUNNEL_BRIDGE | Tunnel entrance or bridge ramp | 
| TILE_CLASS_OBJECTS | Objects | 
| TILE_CLASS_VOID | invalid tiles (map border) | 
