Not sure if this is possible, but is there a way to list all users who specify a given location as their \"current city\" using the Graph API or some other means?
You can search for Users and add fields to query by like hometown or location. The user must have opened their privacy settings though to share location with search.
https://graph.facebook.com/search?q=Marcus&type=user&access_token=
If you see Facebook notification when you try to search but found nothing, it says:
Looking for people or posts? Try entering a name, location, or different words.
You can add location to the query, like: my_name my_location
--> "Aminah Nuraini" Indonesia
It will only work if the user allows people to see their location, though.
There is no way to search for users who haven't authorized your app. Currently the search?q=xxxx&type=user searches only on name (facebook used to allow email, but removed that when they found out bad people were using that search to do bad things).
Impossible, even if the app is authorized.
Here are the fields you can search by (marked with *)
http://developers.facebook.com/docs/reference/fql/user/