An Obstacle is anything on the Mission Map that prevents a unit from moving onto a specific Square. Obstacles also block Line of Sight. Obstacles include walls, Models and Blip Tokens, but not Hazards.
Mission Map
The Mission Map is composed of a number of tiles, often in a configuration of four by four tiles, although other configurations are possible in some scenarios. Each tile contains five by five Squares, which is where the normal sized Models are placed. (XXL Models take up more than one Square.)
When playing the Narrative Mode, the layout of the Mission Map is described in the Mission Book, although some map tiles may be left unspecified; in that case, randomly place map tiles with similar background art in the places where an unnamed tile is called for.
When playing the Conquest Mode, they map is built by the players, but in difference ways depending on whether the Mission type is Liberate or Conquer. See the description of the Conquest Mode for further details.