For Christmas this year I got a great book called Lost London, published by English Heritage. It documents in photographs London in the years 1870 to 1940. The London that the combined might of planners, developers and the Luftwaffe swept away.
I have also spent quite a lot of time, for one reason or another in Streetview, looking around various locations. I even invented a game at home for my kids. I dump them somewhere in Streetview and they have to work out where they are (the best was the Isle of Mull - "Balamory!", the easiest "Grandma's house!")
So what technology has brought us is perfect recall. The tantalising and fragmentary glimpses we see of London 100 years ago or more give us an elliptical glance at the way life was, but the record is incomplete. Streetview allows us to stroll around towns cities and the countryside at will, observing every detail of architecture, town planning, fashion, advertising, automotive design, agriculture and even economic activity.
Which presents posterity with an amazing opportunity. If Google's slightly creepy Streetview vans take a snapshot of our country every 5 years, the legacy for future historians will be immense.
And it doesn't stop there. Mix in the petabytes of social media data generated around people and places that has all ben time-stamped, and future historians will have a field day. Imagine the young Charles Darwin was on Facebook while at Cambridge, or tweeting away his early cogitations. What insight we would have into his world and the way he came to think the way he did, and who might have influenced him. Stepping back into Streeview, Cambridge 1829, we'd be able to walk the streets as he saw them.
Which means, I guess, be careful what you write, wherever you write it. You never know how you might get entangled in future history.