I think I read somewhere that neighbouring civs would be culturally close to your own civ (that is correspond to the real world situation) so that for example Americans, Iroquios and Sioux starts close to each other. I also think this was actually the case in version 1.12. I've been playing 1.15 lately though and then I always seem to get those weird neighbours. For example in my last game I was Babylonian on a continent together with Zulu, Portuguese, Japanese. On another continent was French, Mongols and Sumerian. Wouldn't it be more logical for the Sumerians to start closer to me than the Japs and the Japanese to be closer to the Mongols??