At some point within the past few months, Google Earth has added the option of "historical imagery". Its great: you can overlay historic maps on the area that you're looking at, adding the ability to compare the now versus then. It's fun to play with for a while and worth trying out, but it doesn't approach the scale that I'd been hoping for.
To any of my friends that would listen, I've been advocating for the past couple of years the idea of a fourth-dimension element to Google Earth. The idea hasn't been implemented with this latest update, but it can't be far from being realized: ideally a user can tag a location with a time frame, and subsequent users can see that tag when accessing a range that includes that time frame. For example, I can currently tag the location of the Portland Hotel, but if I tag it, it shows Pioneer Courthouse Square. There's already a ton of tags on Pioneer Courthouse Square, and it's difficult to parse through them. Ideally, I'd tag that site with the dates of its existence (1890 - 1951), and if someone used a slider bar between those dates, only then would my Portland Hotel tag would pop up.
I've got a ton of data that I would love to tag using Google Earth, but I hesitate to contribute, because I feel like I'm making noise. The program as it is exists is an amazing way to view a site unseen by you, but who needs all the extraneous data on the history? I'm only thinking of Portland here, as it's my focus, but what about more historically important sites? I'm thinking of places like Trafalgar Square in London, Tiananmen Square in Beijing, or Union Square in New York. Many things have happened at these points over the ages, but they might not be immediately important to the casual virtual tourist. Perhaps it's important to someone to know what was on exhibit on the Fourth Plinth in 2000 to a few people, but probably not to the casual internet tourist.
On the other hand, site-and-time specific data could be a huge boon to historical researchers. For example, I have a specific Google Maps set dedicated to Portlands buildings in 1908. Maybe someone else out there is interested in the city of Portland during 1908? What a boon it would be to the both of us to be able to set our slider bars to "1908", and only see, tag, and markup that year. Granted, this is is only useful to those interested in the past, but what if this was implemented globally? It would provide us with another tool of understanding the past that has brought us to the present.
With our technology becoming increasingly friendly to geotagging, this idea may be even more important. It might not matter now how many first kisses happened in Pioneer Courthouse Square and how they're tagged, but in a couple of years, there might be a critical mass. Tiananmen Square might be the site of hundreds of thousands of geotagged Facebook updates. It's all noise and unwanted distraction now, but by 2049 it might be the answer to how we lived our lives, one location at a time.