edit: if there are 2 or more persons living in the same city, you can only see one if you click that city on the map. but sure, you can browse the list for the city to see both, but that's a bit annoying.
Check the shadows of the marks. The darker, the more people live in that city. But I know, it's not very comfortable, though I can't think of a method to make more than one person in one city easily noticable. Suggestions?
Added you btw :)
Edit: Okay, I'm using a different kind of mark for cities with doubles now. Tell me if you like it :D