As the name of the game suggests, appoint a country and / or city to the avatar above you based on their profile picture and where they'd appear to reside in. If their pfp isn't enough, you can also draw inferences from their signatures.
For example, because the Sim in my avi / signature appears to be tech-savvy, the Simmer below me can choose to appoint her to "Santa Clara, California, USA." Because it is located at the centre of Silicon Valley.
I've always imagined @SupersonicAvalanche
's Avatar to be from Seoul, South Korea and @AlpineCuriosity
's Avatar to be from Milan, France.
So have at it!