Flickr have just launched Places – which is basically a way to explore Flickr via geo-specific pages. Each page includes a map of the area, the most interesting photos, a tag cloud, photo groups and, for towns, the current weather. But that’s not the most interesting thing about Places – the most interesting thing is how they implemented their URLs.

Creating a good URL schema is not easy. As Michael, a colleague of mine, reminded me “good URLs should be persistent and hackable, but most importantly they need to be persistent”. This is because if you can’t reliable point to a resource you can’t join it to other things on the web, you can’t add context to the resource, you can’t manipulate it. And if you can’t do that then the webpage is no more than a piece of brochureware, it’s not a web 2.0 citizen.

Now the folks at Flickr have done a great job of creating persistent hackable URLs. What they have done is created a URL schema that looks like this:

flickr.com/places/:country/:territory/:city

Which for London is:

flickr.com/places/United+Kingdom/England/london

These URLs are easily hackable – for example you can get to the England page at this URL:

http://flickr.com/places/United+Kingdom/England/

Even if some of the URLs are a little US centric.

Now to pull this off is very impressive. As Dan Catt explains:

…turning essentially a record ID from the backend into something that a human can understand, and yet the backend can once more turn back into the same record ID wasn’t as easy as I thought it aught to be when we asked Kellan to do it : ) and lots of effort went into making it so.

Basically you have to ask the backend, where something is the ‘child-of’, to build the hierarchy. However as we don’t have full control of the backend you often get a city, let’s say London, belonging to a place called Greater London, which, as far as I can make out from the bounding box, is about 2 inches taller and wider than London. Or York (in England) belonging to something like Duke Elligton’s Marginal Lower Land Barrows of the Kidsworth Council Academic Elective Region. Because that particular piece of geographic data was extracted from the government’s parish records from 1895. It wouldn’t surprise me to find that some towns in England were a child of a mobile library’s service region.

Anyway, hidden away from me in a black box constructed by Kellan and Aaron is all the complex magic that works out what’s important and what to miss out.

All very impressive.