bioelectricclam said:
The dotted lines represent the edges of the map. Does this help any?
See, going north doesnt mean that you are suddenly on the south edge...it means you have crossed the horizontal line in the illustration. Same with the sides.
My argument was not with your assertion. Sorry for the confusion.
My argument was aimed at the notion that SOMEONE ELSE POSITED that travelling north on a toroid caused one to reappear on the south now traveling north.
Here is my point, in Civ terms:
If I sail my Caravel up to the North (top) edge of the screen I should reappear at another point that is also at the top of the screen, but either left or right (east or west) from where I left the screen, if I was on a globe represented in 2 dimensions.
IF by sailing my caravel up to the top of the screen I reappear at the bottom of the screen AND if by sailing off the left edge I reappear at the right edge of the 2 dimensional screen, THAT SHAPE is not a toroid, but is a geometric shape that cannot exist in either a 3 or 2 dimensional world.
By sailing up and reappearing at the bottom, it suggest that those two edges meet and are not far apart. BUT, if that is the case, then one should not be able to sail to the left (west) and reappear on the right (east).
In a two dimensionsal representation of Globes, Cylinders, toroids, or even squares, in fact ANY 3D object at all, one need pick one way to wrap around and cannot choose to represent both by having object reappear on the opposite side of the screen from which it departed.
That object as described, where both N & S wrap AND E & W wrap does not exist in the known universe. It cannot be 3 dimensionally represented, and it certainly cannot be 2 dimensionally represented. It can only be represented through non-Euclidian geometric mathematics.
You cannot wrap both N&S and E&W on a two dimensional map and have it reflect any type of reality in the universe. Pick one way to wrap.
bioelectrician: in the image you provided, by going off the screen to the north, one would reappear somewhere else on the northern edge, not the southern edge, and I agree that is what a true toroid is. BUT the argument was made that by going off the upper edge one would appear at the lower edge, and that is incorrect, if one is also able to wrap E & W. That is my point, and I understood it long before you posted the image, no offense.
So, if a toridal map merely means a NS wrap instead of EW that does not make it a true toroid. It really just makes the map type another type of cylinder.