This map visualises the walls based on the sizes given in this eyecatch.

If those numbers are accurate, the walls are absolutely enormous - comparable to all of the various parts of The Great Wall of China combined. The default position is as close as I could get to central Europe without hitting the ocean, and you can see that it's a pretty tight fit.

You can drag the walls around to try to find a better spot (my best guess is somewhere around 54.2395, 42.7587). Given how long it takes the characters to travel around and between the walls though, I prefer to think they either have much smaller "kilometres" than we do, or their military has simply disclosed false information!