The Geolocation Revolution We look at the trend, the apps and what it means to your privacy.

Facebook wants to know "What's on your mind?" Twitter asks "What's happening?" But that's getting old already. The burning question for the next wave of social networking is "Where are you?"--and services like Foursquare, Gowalla, Brightkite, and Loopt want you to use your smartphone to answer it.

The technology at the heart of this trend is called geolocation; and with a GPS-enabled smartphone such as the Apple iPhone, Google Nexus One, or RIM BlackBerry, you can use it to let your friends know where you are, or to find places recommended by people you know, or to check in remotely at clubs, bars, and restaurants. Regardless of privacy concerns (which I'll look at later in this article), it looks as though nothing will stop geolocation.

How It Works
Typically, geolocation apps do two things: They report your location to other users, and they associate real-world locations (such as restaurants and events) to your location. Geolocation apps that run on mobile devices provide a richer experience than those that run on desktop PCs because the relevant data you send and receive changes as your location changes.

Smartphones today have a GPS chip inside, and the chip uses satellite data to calculate your exact position (usually when you're outside and the sky is clear), which services such as Google Maps can then map. When a GPS signal is unavailable, geolocation apps can use information from cell towers to triangulate your approximate position, a method that isn't as accurate as GPS but is has greatly improveds in recent years. Some geolocation systems use GPS and cell site triangulation (and in some instances, local Wi-Fi networks) in combination to zero in on the location of a device; this arrangement is called Assisted GPS.

As long as the sky is fairly clear, the geolocation app on your phone can ascertain your position reasonably accurately. Indoors, however, it's less accurate, and in locales where storefronts are in very close proximity, you may have to select your location manually from within the app interface. Eventually, though, more-advanced A-GPS systems should increase the accuracy of geolocation positioning inside buildings.

The First Wave of Apps
Several start-up companies offer geolocation services--and some, such as Foursquare, reach hundreds of thousands of users. Not only do these services let you share your location with your friends, but they also bring a social gaming element to the table. Let's have a look at some of them.

1. Foursquare works with iPhone, Android, BlackBerry, and Palm (WebOS) phones. If no app exists for your smartphone, you can always use the Foursquare mobile website instead. Foursquare refers to announcing your location--and thus telling your friends where they can find you--as "checking in."
   
   You can check in to cafes, bars, restaurants, parks, offices, and pretty much anyplace else. Once your friends know where you are, they can recommend places for you to go or things for you to do and see nearby. To keep it fun, the service gives you points for each check-in; and in time you can earn various badges tracking your progress toward Foursquare elitehood.
   
   Even cooler, if the service recognizes you as the mayor of a location (by virtue of your having visited that place more frequently than anyone else), you are in for some freebies. Foursquare has a massive list of places all over the world that offer special discounts and free drinks to their mayors, or to anyone who has registered a certain number of check-ins at their site.
2. Gowalla, like Foursquare, works with the iPhone, Android, Palm (WebOS), and BlackBerry (on Bold, Curve, and Storm phones) platforms. The service has a huge database of locations curated by users, and you and other participants can trade virtual items that you've collect. Gowalla also has worked out several advertising partnerships that enable you exchange virtual goods for their real-life counterparts for free.
   
   Gowalla recently added a trips feature (iPhone-only at the moment; Android and WebOS versions coming soon) that lets users recommend up to 20 locations that they like to other Gowalla enthusiasts. Your friends can then complete the trips, such as city tours or bar crawls.
3. Brightkite works with iPhone, Android, Palm, Nokia, and BlackBerry smartphones. This service lets you establish two kinds of social connections: fans (Twitter-like followers) and Facebook-like friends. Aside from sharing your location, you can post short messages that your friends or fans can respond to with a thumb up or thumb down.
   
   Brightkite has excellent privacy controls that let you share individual posts with everyone or with friends only; you can also cross-post on Facebook, Flickr, and Twitter. Like Foursquare and Gowalla, Brightkite uses the check-in system for bars, clubs, museum, and the like, and it finds your location automatically.
4. Loopt , which combines geolocation with social networking, is available for the iPhone, BlackBerry, Android, and many other phones (full list). Like other services, Loopt invites you to check in to locations and share what you're doing with Facebook and Twitter friends, next to your own network of Loopt friends.
   
   Loopt also provides an event directory called Pulse, where you can browse various listings categories (such as movies, gigs, and shows) for things going on near you--and afterward leave ratings and tips. Freebies and special offers are available too, indexed from nearby retailers.

Google, Facebook, and Twitter Join the Party
With such a burst of interest in geolocation, it's hardly surprising that social-networking giant Facebook and ever-growing Twitter are getting involved. Last year Twitter introduced its geolocation API, which allows third-party developers to incorporate the feature into their apps. Many Twitter smartphone clients, such as Twitterrific or Tweetie, nowadays let you attach your current location to your tweets, and so do some of their desktop counterparts.

Twitter has recently introduced the same feature on its website. Using geolocation from Twitter.com is not as seamless as with services like Foursquare or Brightkite. First, you have to opt in to the feature, and currently it works only with Mozilla's Firefox browser. The Twitter service lacks check-in features and offers no incentives, such as badges or points, when you share your location. Right now, the only way to view the location information attached to a tweet is via a Google Maps overlay; but you can use Twitter's advanced search mode to search for tweets from around a certain location, such as a city.

Facebook is expected to make geolocation features available to its 400-million-plus users sometime in April, though details of the implementation remain undisclosed. Given that more than 100 million Facebook users update their status from mobile phones, however, the potential popularity of geolocation on that network is huge.

Google hasn't been idle, either. In February, the search giant introduced a new geolocation and social networking tool called Google Buzz. Buzz resides within your Gmail app (under a new tab) and allows you to share status updates, images, and videos with other Buzz users.

Google Buzz is also available for use on Android phones, as well as on the iPhone, via a Web-based application. The mobile version lets you post (or dictate) real-time geotagged updates to your Google Buzz feed that show up on a new version of Google's mobile maps. The maps also show the location-sensitive updates of other Buzz users in the area.

For its part, Nokia offers a geolocation service through the Ovi Lifecast widget on its N97 and N97 smartphone models. (rumor has it rumor has it that Apple will integrate the app in a future version of the iPhone).

Even the Mozilla Firefox browser can tell websites where you are located, so you can find more-relevant information.

Google has also integrated location sharing in the latest version of its Chrome web browser. Chrome's feature uses the World Geodetic System (WGS 84) navigation system, which is the reference coordinate system that the Global Positioning System (GPS) uses.

Geolocation and Your Privacy
When you leave your home, you inevitably sacrifice some of your privacy; and by sharing your location on social networks, you could put yourself at some increased level of risk. But geolocation services are working hard (without always succeeding) at keeping you safe from the potential dangers of sharing your location publicly.

Most geolocation apps let you set a certain level of privacy, but you can never be too wary of people with bad intentions who may be following your updates. As a first step toward protecting yourself, it's a good idea not to expose your home address on these services.

Privacy advocates have already gone to great lengths to raise awareness of the dangers of location sharing. One example is the PleaseRobMe.com website (now retired), which aggregated tweets with location data attached, to highlight the dangers of having thieves invade your home when you tweet a distant location.

Unfortunately, keeping your whereabouts hidden from other people defeats the purpose of geolocation, so you have to make sensible decisions about how widely you share your status and how carefully you guard your privacy settings.

Brightkite, for example, lets you select for each post whether to share it only with your friends or with the whole world; however, if you cross-post your location on Twitter, any ill-intentioned follower could use that information.

Twitter's approach to geolocation, in contrast, lets you select whether to include your whereabouts for each individual message. Google Buzz does the same thing. Twitter also lets you delete your entire geolocation history, in case you change your mind and want to erase your tracks.

Where Is All of This Heading?
Right now, geolocation apps seem to be the province of hip geeks and other tech enthusiasts. They also seem to be mainly about fun: Without the gaming features that Gowalla and Foursquare add to the technology, those apps wouldn't be nearly as popular. But as geolocation technology gets better and more precise, it may prove to be extremely useful in more-serious apps, such as those used by public safety and news-gathering professionals.

But as more apps, fun or serious, begin attaching our locations to our messages, related privacy issues will remain a hot topic of conversation, perhaps forcing us to reexamine our views about how much privacy we need to maintain in our digital lives. As Facebook CEO Mark Zuckerberg has suggested, privacy isn't what it used to be, and many people may be willing to surrender some of our online privacy in return for increasingly smart, convenient, and enjoyable apps.