I'm a real history buff. Not so much Kings & Queens, battles and treaties, but the more local kind - wandering down a street and knowing that the building to your left used to be Thomas More's and was known as Crosby Hall when it was in Bishopsgate and that sometime around 1910 it was moved, brick by brick, to where it is now (by the river in Chelsea); or that the name "Flood Street" which, although by the river, in fact derives from Thomas Flood. Or that Christopher Wren might have lived in a house on Cardinal Cap Alley, next to where the Tate Modern is now, but probably didn't. And don't get me started on St Paul's Cathedral; I'd be posting all night (although this layout that Wren planned for post Great Fire is worth looking at). When you work in government, you get to see some amazing stuff, quite by chance, like the inside of the Cabinet Office (which still has original walls from Henry VIII's "Whitehall Palace"), or the inside of the Houses of Parliament - you can all go and see it but how many Londoner's have walked in through the St Stephen's chapel entrance and realised that the short room immediately before you - about 50' long - was the actual site of Parliament when the Palace itself was used for other things (you'll see it as St Stephen's Hall if you click the previous link)?
So, as a history geek, I'd really like to see a version of Google/Windows Earth - or even Google Maps - that stitched together as many old maps as possible from earlier times and allowed you to layer them on to a view. Alongside that, instead of the little blue dots linking to photos uploaded by users, they'd link to copies of pictures drawn, sketched, photographed or painted at the time that the map was done. Better still would be same 3d models of old buildings, based on the data available.
As I walk the streets of London and see yet another building being demolished or, more often, a hole in the ground where a building once stood, I wonder what used to be there. It's difficult for me to remember what was there even 5 years ago unless I visit the area regularly, let alone what was there 20 years ago. Piecing together the history of what was there before the 2nd World War, before the Victorian era, or at the time of Henry VIII would be truly fascinating, educational and, quite probably, inspirational. We don't have satellite imagery of course, but we do have an impressive collection of documentation and maps that you can find rendered all over the Internet, albeit you will struggle to bring together a comprehensive view.
Maps like this one can bring so much to life. The London Embankments (orchestrated by Bazalgette in the late 1850s, are yet to be seen), buildings run right down to the river, there's no Southwark Bridge, no Cannon Street station. When was all this? 1801. Want an earlier one - then here's a copy done in the 1850s of one from the 1520s or 1530s. Or to bring a bit of perspective, a panorama from the 1845.
Imagine seeing this all stitched together, segment by segment, laid over an up to date map, scaled properly and easily navigable with just a mouse and the occasional click!
A while ago, 2001 or so, before they had much online presence, I talked to the British Library about what their plans were for digitising their archive. This was one of the ideas that I wanted to explore with them but it would have been tough to achieve in the dial-up dats. With Google Earth/Maps, the Microsoft equivalents and plenty of other tools, it seems like it is actually achievable and maybe even relatively simple, at least for the big towns, now.
Dan has since added two ideas to the mix:
(1) rolling the mouse wheel should zoom you back and forward in time
(2) why not start now? there must be a huge archive of satellite material for at least some areas, so why not add the ability to see how things looked just a few years ago? In an age of increasing worrying about climate change, the ability to see how, say, Lake Mead's area covered has changed over the last decade would surely interest many