@Rick (OS maps the details)
> OS, on the other hand, map everything. And I mean absolutely everything.
> Roads, paths, buildings, heights, pylons, fences. Everything. Oddly enough,
> measuring and recording everything in such detail costs money, and involves
> actually looking at the place rather than just sitting at a computer. Good luck
> getting that done free over the internet.
You would be surprised how cheaply you can precisely map these roads, paths, buildings, heights, pylons, fences and everything with current technology. Let's do one example:
Let's say you have 2 Google Streetview Images of a standard postbox. The images come with GPS coordinates, so we can derive that they are for example precisely 20 meters apart.
Now we also know the camera orientation (Google is to lazy to align these pictures by hand, so they probably record compass data). We also know the optic properties of the camera (if Google doesn't tell us, there are millions of pictures to derive them from and I am sure they photographed a few mirrors here and there).
We also know how big a standard postbox is.
Ergo, with some trivial math, we know exactly *where* the postbox is.
Now all we need is a couple of people who tag every postbox in the city, which is virtually no work. In fact, if you do it for a couple of hundred postboxes, it should be a trivial to let a computer find the other hundred thousand or so in the country.
Once we know the size and exact location of several typical objects, we can calculate the size and position of everything else in the image just by looking at the geometry.
So you next question will probably be, how are we going to maintain this stuff? Don't we need a big expensive agency for that? Well, your government is solving that by putting up CCTV cameras all over the country. You can track every fence and every postbox in the country, every second, every day. And it will barely cost a thing because its payed from the anti terrorism budget anyway.
And there is all the amateur cameras with GPS. In fact, even camera's with no GPS will do here. Thanks to Google, we now have an approximate image of everything and it should be "easy" to match the pictures to them.
While we are at it... Does anyone really believe that face blurring is going to be enough once every street in the country is monitored at every second of the day? With that much data, I think you can derive peoples identity from their cloths, the way they walk, etc. And the photos on FlickR don't do face blurring... Fascinating, albeit a bit scary.