Update: some reports now saying the crowd was around half a million people in it. Looking at the intensity of tweeting it seems possible.
Tracking tweeting in London can be difficult because of the heavy background nose of day to day tweeting taking place in London almost all the time. We have developed a HD tool to do just this. With this tool we can pinpoint very precisely location of very recent tweeting.
Using this HD Twitter tool we see a very large group of people forming around Embankment and Parliament east of Hyde Park. We will be watching to see if the group moves west towards Hyde Park. We assumed from this cluster and the high activity around the Twitter hashtag #26march that we will be seeing a massive protests today in central London.
London Protest-Photo By Gail Orenstein-web 3.0 lab/Clima
UPDATE: We are now seeing the media reporting that 300,000 or more may be converging on London. We have also seen Twitter local to London going doing some as the crowd seems to have crashed it with tweets. This protest today may be the largest event in twitter protest history.
We are seeing levels of high concentrated tweeting around the start of the protest now that we have never seen for any location anywhere. We are some some of the most concentrated tweeting in one location for one event we have ever seen anywhere, including Tahrir when Mubarak fell. In fact the numbers are blowing anything we have ever seen in Egypt out of the water.