I came across this really clever use of twitter this morning as London got it's first snow flurries of the season. #uksnow Map 2.0 monitors twitter for mentions of snowfall, then plots the snow on a google map. To make best use of it, you need to use a special tweeting convention – insert #uksnow followed by a postcode and 0-10 rating (0 being nothing, 10 being a full on blizzard) – for example, #uksnow SE1 2/10.
This reminds me of a pilot I set up at BBC Leicester, where we loaded some 3g mobiles with Yahoo's Zonetag and asked 5 members of the public to contribute a few weather photos each day, directly from their handset, to a flickr group that automatically fed a BBC template page.
It would be interesting to see the #uksnow map displaying images from twitpic and I can imagine all sorts of uses of this – flood monitoring, disaster relief, coverage of the Olympics, etc.
See the #uksnow map here: http://uksnow.benmarsh.co.uk/