I'm considering making a few minor modifications to the map, mostly to redraw some images to more accurately represent coastal areas. However, there are a few state boundaries that nag at me and I'd like to split a few regions along the state lines that cross them. However, there is at least one important question I don't know the answer to, and that's how the travel time is determined between regions.
Not counting the special regions like California and Arizona, and assuming that I converted all regions to clear terrain and it's always nice weather with no rain, snow or mud; not crossing a waterway; and using the same element in each case: does it take the same amount of time to travel between any two adjacent regions, or is there distance data incorporated into the region files that make it variable depending on the regions?