Looks very good. And what a huge map.
And BTW it is Medieval not Mediaeval.
I don't know anything about wxWidgets but using pure Windows API you would create a memory DC and a screen DC. Draw to the memory DC and when done drawing blit the memory DC to the screen DC.The MiniMap flicker is awful and needs to be fixed. This is actually an excellent oportunity to study about those clipping techniques.
As for clipping regions you can use the Win32 API equivalent of InvalidateRect() if you do not wish to redraw the entire map every time a movement is made. You just Invalidate a small rect area around the hexagon or hexagons that you need to update. Then when your paint or draw function is called it will only update those invalidated rects. I ran into this with my tile editor quite often and this solution helped a lot.
