Sullla is a little bit off in his analysis. The arrows are irrelevant; opposition on a torus is a flawed concept. If Sulla sailed due northwest (his white arrow), the ship would miss the donut in the northeast corner, cross over the north edge, and intersect the donut again close to Broker. (The line would be a "Great Diagonal", the analogue on a torus of a Great Circle on a sphere.) The shortest distance over water from Sullla to a neighbor is actually IKZ.
Anyway, opposition is also irrelevant because Civ 4 treats diagonal distance the same as orthogonal. If Sullla were to sail a boat due west, it would reach IKZ in the same time as a boat sailing southwest would reach Mortius's start location.
Sullla is thinking as if a civ reaches another by superimposing a circle (the area traced out by a straight-line segment as a radius) on a sphere. But the actual geometry is that of superimposing a square (since Civ units can move diagonally) on a torus.
Not that this is likely to have any practical impact, though.
Anyway, opposition is also irrelevant because Civ 4 treats diagonal distance the same as orthogonal. If Sullla were to sail a boat due west, it would reach IKZ in the same time as a boat sailing southwest would reach Mortius's start location.
Sullla is thinking as if a civ reaches another by superimposing a circle (the area traced out by a straight-line segment as a radius) on a sphere. But the actual geometry is that of superimposing a square (since Civ units can move diagonally) on a torus.
Not that this is likely to have any practical impact, though.