If we take equator radius (6,371 km) and divide it on a Huge map (128 tiles), we get each tile would be around 50x50 km.
You are not really playing on an earth-like planet, you are playing on a hypertorus of some sort (like a "donut", except the inner circumference around the hole is the same as the outer circumference around the entire thing - something that is not possible in only 3 dimensions).
I was wondering what the scale of CIV is, what the dimensions of a single tile are. Does anybody know?
Actually, you can get a pretty good approximation in only 3D. A wide wedding band for example, would be pretty close to this type of mapping.
Only if your map is cutting across the interior of the planet. It is not the radius you want, it is the circumference. So you are off by a factor of 2*pi, so it is closer to 215 km if your radius figure is correct.
According to the demographics it seems that each tile is worth 1000 square km. So based on that the tile dimensions would be 31.6 x 31.6 km.
I have always been under the impression that units did not represent any single unit, squad, brigade or army, but rather represent a certain number of soldiers expressed in the Demographics screen.