earthTwitter finally rolled out its new application programming interface for tagging tweets with your location.

It won’t appear on Twitter.com, but it will be enabled for location-based services like Birdfeed, Seesmic Web, Foursquare, Gowalla, Twidroid and Twittelator Pro. Tweetie already switched on some geotagging functionality earlier this year, so you can see nearby tweets.

This is probably the most significant update Twitter has released in the last half-year and it’s hard to say what outside developers will come up with. You can bet that a lot of it will be centered around entertainment — figuring out where your friends are and what’s going on at night. There probably will be many news applications as well, so you can see tweets from first-hand witnesses. This should also strengthen Twitter’s upcoming location trends feature, which shows you what’s popular in different cities.

Twitter’s Ryan Sarver wrote:

Now you can find out what live music is playing right now in your neighborhood or what people visiting Checkpoint Charlie are saying today about the anniversary of the Berlin Wall. These are only the beginning and we are really looking forward to seeing the creative uses emerge from the developer community.

You can turn it on by visiting your profile settings and checking the ‘Enable geotagging’ box under your location. You can also wipe out your location history in case you want more privacy. (However — independent applications can store this data too and it’s up to them to develop their own policies on erasing data.)

Tweets are tagged on a case-by-case basis, so you have to opt-in every time you want to reveal your location.

geotagging

There are a few key practices Twitter is also pushing its developer community to embrace —

  • Geo-tagging must be opt-in. An application can only share data if a user explicitly says it’s OK.
  • It must be clear every single time a tweet is being tagged.
  • Developers should be clear about how they will store historical location data.
  • Apps should promote the discovery of other Twitter users.
  • Developers should account for the fact that international mapping data is imperfect.