The area put forward for certification has to be a space that can be closed off completely, bounded by its walls, doors, windows, floors and ceilings, and its doors and windows must be capable of being locked or secured some other way. The guideline notes that these surfaces form the physical containment barrier around the GMO dealings, protecting every space outside the facility, other parts of the same building included, and the environment.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.