I have a GeForce 650 TI. Since the game released I have this bleeding grid lines issue with hiding hexes beyond the cultural borders or full grid lines. Here is a screen shot.
http://screencast.com/t/NggzeEW9
Orientation of the map does not make a difference. There is a faint flicker to the lines when I pan the screen. I was playing on my laptop and I don't have this problem. The grid lines stop at the cultural borders. So I'm guessing it's having drawing issues.
