Distance is not covered in the core rulebook at all (that I can find). Without knowing how far it is from town to town and the speed a mouse can travel at (depending on season) how do you set the Obstacle for a pathfinder test, for example? How would you decide a Journey conflict is needed rather than an Obs test?
Does it matter? Is distance largely irrelevant?
Distance is one of the factors into determining the Pathfinder obstacle, although it is abstracted.
Pathfinder Factors
Destination: Nearby, a short journey, a long journey, remote or isolated
The GM should choose which of these seems most relevant. There's no explicit speed listed or distances involved. The map doesn't even have a scale.
Refer to the conflict rules as to when travel might be a conflict.
Sometimes a moment is so important, we need to stop and focus on it.
In the game, we use conflicts to create those intense, detailed situations. These are the turning points of a story. Use them for big, important moments.
A conflict scene needs active opponents on at least two sides. Each side must want something. They have to have an immediate goal.
For example, it's not just getting there, but getting there before the weather turns bad leaving you stranded or worse, or in time to deliver the medicine before more mice die, or with the dignitary's safety in mind.
(All quotes from the first edition.)
I've been crunching numbers to answer this exact same question as it's come up for us as well. Regarding land speed, my best estimate is that mice manage about a mile a day (a mouse at 3-4 inches tall stands roughly an 18th the size of a 6' human; humans manage roughly 20 miles a day--dividing that by 18 you get pretty close to 1). It makes a handy conversion since the math is tidy.
So mice can travel roughly a mile a day. What's that do to the map scale? It's mentioned that the trip from Lockhaven to Sprucetuck and back in seven days is a tough trek. That tells us a fair bit. If we take a look at the distance between Lockhaven and Sprucetuck--it's about 4" on the map, if an inch is a mile then that works pretty well--it would mean that the whole round trip would normally take 8 days, which could be shortened to seven if the characters hurry--if nothing goes wrong to delay them, but it's winter, so everything takes longer. That seems about right.
So according to what research I've been able to do, it looks like the travel rate for mice in Mouse Guard is about a mile a day and the Mouse Territories map ends up at a scale of 1' = 1 mile. There's certainly wiggle room, but that seems to fit and is nice easy math.
