OK, so it's not exactly new. GPS has been helping people discover where they are, where they are going and where they made a wrong turn for some time. But really, that was just the start.

For one thing, GPS has now emerged from the car/boat, got way smaller and become portable. I run most days (hard to believe if you know what I look like) and use a Garmin Forerunner to tell me how fast I'm going (not fast enough), how far (not far enough) and how many calories I've burnt (just enough for a guilt-free breakfast). It wasn't so long ago I was reliant on a piece of string, a map and a stopwatch to plan and track my runs (BTW check out MapMyRun for a nice Google Maps-based app for working out your run in advance).

Earlier this week, Flickr announced its new (non-GPS) geotagging feature. This allows you to tag a photo with its location (using a mash up with Yahoo Maps). On their blog, they say they expected to hit a million geotagged photos in the first month. They actually hit 1.2m in the first 24 hours. Of course, geotagging relies on the user telling Flickr where the photo was taken (which, admittedly, is pretty easy). But what if it was simpler than that?

Which brings me back to GPS.

Earlier this month, Sony announced the GPS-CS1.

This is basically a clip-on GPS receiver for photographers. Attach it to your belt and it'll record where you go on your photography trips. Then, when you upload photos from your camera, you can sync them with data from the GPS unit and, using a Google Maps-based app, show when and precisely where you took each photo. Very clever indeed. (And this is just the start – with Flickr releasing the API for their geotagging, expect to see some interesting hacks in the very near future. Also check out Zoomr for a photo sharing site that already uses geotagging and which might be the natural extension of the Sony system.)

For us in marketing, GPS-based activity is an intriguing prospect. This could be (as is already happening) digital bus-sides showing contextual messages based on location. Or it could be around facilitating user communities – find others like you, near you. It could be around geocaching-style treasure hunts or a whole host of things no one has thought of yet.

This could get very interesting.