APRS (Automatic Packet Reporting System) is used for the transmission of position data in ham radio. As an example, the position data delivered from a GPS receiver is transmitted in APRS format over a simplex frequency via packet radio with 1200 baud. Other stations then could decode this data and mark the position of the transmitting stations with a corresponding symbol on a map. For an increased range, digipeaters, e.g. with the DIGI_NED software, could be used, which retransmit received packets on the same frequency following certain rules.
Stations with data packets that make it into the internet via digis and gateways, could be followed worldwide on www.aprs.net with an Java applet. A similar service is available in middle Europe for the traffic that is seen by DB0LJ, this could be reached via www.aprs.de . With that newcomers to APRS could get a first overview of a part of the activities.
Also www.findu.com should be mentioned to search for specific stations. With http://map.findu.com/DB0AJW you would get the last position of our Berlin digi, of course only if a packet from RF can find its way into the internet. Similar you can do this with every other call, an optional SSID has to be named explicitely. The maps from maplblast that are used by findu.com now have street details even for Germany.
I have put together some extended pages for the following themes: