Ere we go 
Spot the missing pixel 
Your map, in southern Leinster at least, doesn't seem to match up with Gully Foyles district discriptions, but the missing pixel is clearly one pixel before the "local" southernmost point in the boundary between County Carlow (or a district that looks very much like it) and County Wexford (ditto), coming from County Wicklow (ditto) going southwest before turning to the northeast and then going southeast again until it intersects with County Kilkenny (or, again, a district that you have drawn to look very much like it).
Simple really.
I didn't enlarge the map or anything like that, although I did go to Wikipedia for a county map of Ireland to identify where the missing pixel I saw was.
