The starting bias is the setting (you can disable it in game set up) which allows your civilization to have a starting point similar to its original historical location. Like for instance if you play for ottomans you would start in a desert or if you play for iroquois you would start in a forest. So what is this bias for other factions?
Also, how does it work, is the part of the map generated specifically for a certain civilization, or is it generated randomly and then the best fitting spots found?