Since our maps vary greatly in size I`ll have to describe it myself by giving a few examples from standart skirmish gameplay.
Map with two player towns on it would be around 6 by 6 max zoomed out screens.
Map with four player towns - 9 by 9.
With 6 player towns - 11 by 11.
With 8 - 13 by 13.
Quite epic, but not quite in a Medieval Total War scale. We do have huge cities, but realism of our world had to be limited by the travel distance between the cities, so we had to cram things in a bit. Our limit is 1.5 minute long walk between enemy towns, or 45 seconds run (but it`ll exhaust your soldiers)