Another thing to think about with scales is that they don't always need to be in "distance". Now, if your going to do "time to travel", you then have to consider some basic questions. Example, two locations may be exactly the same distance, but the travel time could be greatly different. For example, it takes 12 days to get from Ravensboro to Hillcrest by horse. But takes 22 days to get to Irongate even though they are the exact same distance as the crow fly. The difference is that Ravensboro and Hillcrest are both on fairly flat land, but Irongate is fairly deep into the mountains and this slows travel quite a bit. Of course, on this type of map, it would make more sense to put travel time on each route instead of a central location since it's so variable.