You could always just use the rules for diagonals on page 252 of the DMG

I think that’s plausible, but the boardgame and the video game are very different. If the video game is descended from the board game the change of medium made some big changes. The board game has a big emphasis on trading that the video game cannot reproduce. And the board game doesn’t have individual city management.

I haven’t been on there in a long time but the link below has a way to play it online. http://civ.rol-play.com