We won't see a city's borders until we see it through the fog, even if we've already explored there. So it could be anywhere that's fogged out. And since the river that runs through Old Sarai and Ning-Hsia goes to Berlin, all of our cities hooked up to our national network (which would be all except Kora) have a possible route to any city connected to Berlin. The same is true with Russia's internal trade route.