Great General Spawns

If a unit was built in city X, and that unit gets the attack that gives you the final points for a great general, does the general spawn in city X? Or is it random?

Great generals usually spawn at random at any city.

Is that in the code, do we know that's it random? I've logged ~1200 hours into the game and I'm wondering if there is a pattern or a reason for a great general to spawn in a city other than randomness. If the code says it's random, then it's random but does anybody know or is "random" just a guess? If I built a unit in Boston and it kills a unit to spawn a great general, does the GG spawn in Boston or is it indeed random?