It's assumed that most maps in BREAK!! come with a Random Encounter chart. These are generally custom built and used to represent various things that would be moving about the same location as the players are. The intent is to make the world seem dynamic and like it's its own place, rather than a construct made just to serve the player character's adventures. The encounters include other wanderers from the outside, as well as inhabitants whose opinions on intruders range from apathy to murderous hostility. Each also has several entries that simply say "No Encounter" - this means the primary Roll becomes a one that determines both if there is an encounter and what that encounter is, if any.
They do function a bit differently depending on the sort of map being used.
Larger scale maps (such as those detailing a region or province) have a Random Encounter Table you consult each time you cross a significant distance during a journey ( this determined by a quick use of the Overland Travel Rules). The sort of encounters should vary quite a bit depending on where you are travelling, but a lot of them are potential allies, built in adventure hooks or the results of other dangers going on in an area that warrant investigation. An important thing is that it's encouraged that the GM cross off an encounter when used and write a new one to replace it to keep things fresh.
Smaller scale maps (dungeons and other adventure sites, mainly) have a chart that represent the mobile inhabitants of the area or other things that might have wandered in. This is rolled on every time characters make a lot of ruckus or spend a significant amount of time in a particular area. Every time an encounter is "dealt with"" (slain, pacified, etc) it's crossed off the encounter chart. Only so many things can live in a particular place at one time, right?
Also important is that there are less stationary encounters in BREAK!! (I.E "6 goblins in room c") so these often make up the bulk of the things player's can run into.
There is more too things obviously, but these are the bits that come to mind. I'm very excited to talk more about these sorts of things once the book is published.