Haiyan Zhang, an interaction designer out of IDEO's London operations, has mapped radiation levels around Japan with crowdsourced data from Pachube, a realtime data infrastructure platform that has aggregated geiger counter readings from across Japan. These feeds come from a mix of local councils, official government and motivated individuals who have connected geiger counters to the internet. They're constantly being updated to give the most recent information.
Haiyan's map provides a color-coded, at-a-glance view, updated in real-time. Measurements above the Japanese government recommended dose limit of 1000 µSv per year (equal to 0.114 µSv per hour) are tagged in orange. Those measurements above the recommended limit are tagged orange.
From a user experience point-of-view, I wanted the numbers to be at a glance, avoiding the extra clicks that these mashups usually ask of the user. So you see the readings highlighted in yellow on the map. The orange circles are coloured based on the severity of the reading (the darker the orange, the higher the reading). Clicking on these circles will also bring up more details about the reading (location, timestamp, millisievert).
Read more about Zhang's geiger map on her blog here.