The key concept is probably that every piece of data in the system is tied to a location and is time-stamped. All of this data is put into its georeferenced wiki (gWiki), built using MediaWiki.

Naturally, because it's a wiki, the Visible Past system is read/write. Visible Past claims to open "read/write capabilities to all clients capable of reading and rendering georeferenced data," such as Google's Maps and Earth, NASA's WorldWind, location-sensitive mobile devices, and immersive VR environments such as Purdue's Envision Center CAVE. It also makes heavy use of wiki content from the likes of WikiPedia, Wiktionary and WikiMedia Commons. Everything is accessible via an Internet-connected device.

The way Visible Past works is as follows:

"...as a user moves through space (virtual, real, mapped), information tied to locations on the earth will be revealed to them as they approach those locations. Once revealed, the information can be edited and resubmitted (to greater or lesser richness depending on the client), consumed, or ignored. see this Demo page for a video clip of the client functionality we're developing."

You can browse by keywords, location or time. In regards to how location and time data is captured, that is done via GPS (e.g. on mobile phones) or through virtual reality locators.

Privacy advocates will be wary about the project's tagline, "Where information searches for you". Because the system tracks your location and time, it essentially follows you wherever you go. This is what many location-based web apps do, such as Brightkite. Although most of these apps ensure that the user has sufficient control to turn off and delete their data if they want to. That's the key thing with location-based apps, the user must remain in control.

In any case, in a learning environment - which is what Visible Past is aiming for - it's probably a good thing if information finds you. Currently, Visible Past has a limited set of models, such as one of Ancient Rome as it appeared in Antiquity (cca 400 AD), however it's a technology to keep your eye on as we move further in a location data based Web.

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