How do trending topics on Twitter work?

[Kumiko]

I'm talking about the trends by location. Where does the data about the trends in a specific location come from? Does it come from the location the users said they were in on their profile or does it come from the IP address of the tweet?

[mmc3]

I would imagine the IP address. For location in your profile, you can type anything as long as it doesn't go over the character limit. Additionally, it is not required that you add a location to your tweets, so it can't always be this. Unless trending topics only come from these people for the area-specific lists, but I doubt it. Hope I helped!