This morning’s Observer column.

For me, the most arresting image of the week was not the photograph of General Stanley McChrystal, looking drawn and ascetic in combat fatigues, en route to his dismissal by his commander-in-chief, but a map of central London showing the underground system. On each line can be seen little yellow blobs. Blink and you discover that each blob has moved a fraction. You can see it for yourself at traintimes.org.uk:81/map/tube/.

The yellow blobs are, of course, tube trains. The fact that they're moving across the map indicates that this is, as near as dammit, real-time information about their positions on the network. And it's public data: you can sit at your computer in San Francisco or Accra and know how the trains on the Central line are doing just now.

How you react to this provides a litmus test for determining where you are on the technology spectrum…