Happn.in is a Twitter tool that shows what people are tweeting about locally in 80 cities around the world.
Drilling down into each city produces a list of several hundred to several thousand Twitter account holders who have self identified their locations in their Twitter accounts.
Visitors to Happn.in can click through to each list to scan for potential Twitter accounts to follow or broadcast their message to everyone in a particular market via their Talk to Your City feature.
Rakshith Krishnappa has also created a local Twitter trends map for Happn.in using their API and Google Maps.
Want to find out what Twitter users are saying in any particular market?
Just click on the push pin and the top 10 subjects being Tweeted are displayed inline on Google Maps.