A network link is like the refresh button on your browser only you can set it to work automatically. The web page above shows trains overlaid on a map of Dublin, the web page updates every second and shows the new positions.

More on Network Links

To complete the discussion started by the video: You are left at the point where to update the KMZ file on the server requires a manual update, from where the network link on your copy of Google Earth updates every hour (or however you have it set up to update). What is possible is to get a GPS (Global Positioning System of which a Sat Nav is an example) to talk to the server and automatically update its position. Thus, if I was wearing a GPS it could be constantly updating its position to the server and you could see where I was pretty much in real time.

Harry Potter becomes real

With wireless, hand held devices and the concept of Network Links several of the devices in the Harry Potter books become possible:

The Weasley Family Clock: This clock shows the locations of all family members such as 'Home, school, travelling, hospital, prison' all of which could be programmed to be produced given existing software and hardware. 'Mortal Peril' and 'Lost' will be more difficult to produce.

The Marauder's Map: Shows locations of people against a background of Hogwarts school. A lot of similarities to the Dart map above.

Both these devices are obviously useful in real life so expect to see them develop in the near future. The downside to them is the obvious problem with privacy that will need to be bridged.