After a test roll-out last week, Twitter's just added a new system that displays the Tweet trends  that are most relevant to your particular location. It's an experiment in location -based news discovery, and it could make Twitter very powerful indeed.
In a posting on its blog announcing the news, Twitter also explains exactly why it's augmenting its already-powerful trends feature with a localized version, beginning with talking about why Trends are important: "Trends began as a way to she light on popular conversations [...] help us discover which of those topics are paramount on a global scale." But as Twitter evolves, and its users evolve their use of its systems, "and more people share what's happening in their own world, we want to provide another way for people to discover topics that may be relevant." And the way Twitter's chosen to do that is to let you refine the trending topics list presented under your user data on its home page to a list of topics trending nearby.
For the time being, this system is very limited, and it only works to limit the trend list to that of seven different countries and 15 different cities around the World. But it certainly does work. As I write this, the top three trends worldwide are "#now playing," "tvxqbreakout" and "Apple Tablet" but if I constrain it to Seattle I get "#tw2mu," "iPad," and "iTablet" (I wonder why those last two are there?). Meanwhile Londoners are discussing "#LT10UK," "nowthatsghetto," and "mangojuice" with "Twitter local trends" in fourth place. Clearly each city and nation will have topics that interest it the most at any one point in time, and Twitter's simply giving you the ability to filter Trends on this basis.
And while that reduces the new feature to a pretty basic description, it's actually more powerful than that. Remember that one of the most exciting ways Twitter is distinguishing itself on the social network scene is as a news discovery vehicle. It's partly why its real-time feeds are of such interest to Google . And with the new localized system, it effectively lets users turn Twitter into a local news discovery system, which many may find far more useful. Twitter itself plans to improve "this feature over time t provide more locations, languages and data through our API" which means it sees the system as important, and this news also means local trends will be available through Twitter clients on your smartphone--aided, no doubt, by the newly GPS-taggable Tweets.