Each level is broken up into sets, which are usually large regions of a the map. These are not the same thing as '[[Room|rooms]]' - generally there are a lot more rooms. When a guard needs to plot any route, they first "zoom out" to the level of the sets. They look for a path visiting the least number of sets to get from their set to your set.
+
+
So on Bunker 2 here's the relevant part of the map broken up into sets: