From the Modders Guide to CTDs:

Scrolling over campaign map:
- Not enough province/settlements on a too large map (fix : add provinces on the map/may be fixed with BI) causes CTD while scrolling the map.
- Error with the rebel faction/settlement owner and or creator (when you scroll over a given settlement)
- Some hidden resources can cause CTDs when you scroll over the region.


https://forums.totalwar.org/vb/showthread.php?58801-A-modder-s-guide-to-CTDs