TECHNOLOGY Project participants are equipped with a portable trace-unit. It consists of a small handheld computer, known as a PDA (Personal Digital Assistant) in marketing terms. The PDA, with a built-in telephone, is connected to a GPS-receiver and an antenna to match. The PDA can be carried around in your hand or in a bag, the antenna (the size of a matchbox) needs to be worn (or stuck to e.g. the roof of a car using the magnet) in such a way that is has a good line of "sight" with satellites. The software developed for the PDA activates the GPS (Global Positioning System)-receiver. By doing a triangular (timing) measurement the receiver determines its position on earth and comes up with the participant's location. This metod results in coordinates with a maximal accuracy of five to seven meters. On the small screen of the PDA these coordinates are translated into pixels, so that the participant gets a visual impression of the route he's taking. The PDA-software developed for the project maintains an always-on internet connection to a server at Waag Society and non-stop transmits the resulting coordinates in realtime. Ths is taken care of by having the built-in telephone set up a connection over the GPRS (General Packet Radio Service)-network. GPRS is the so-called 2.5G network, where G stands for Generation, and is an inbetween technology between the current GSM-network and the 3G UMTS network. It's not a broadband network yet in the way UMTS promises (?) to be but has a higher bandwith ans enables for internetconnections. It is e.g. the GPRS-network used by Dutch provider KPN to launch their new "I-mode" services. At the Gemeentearchief (City Archive) a computer (client) is set up with Keystroke-software developed by Waag Labs which fetches this data, again in realtime, from the server and through the use of a beamer projects it in the exhibition space. This software renders the participants' routes realtime as traces, slowly but surely causing a map of the city to be constructed. Spots on the 'map' which are visited or crossed often, gradually change colour from white to yellow to red, showing the 'intensity of use' of routes or locations. The projection is influenced by visitors going into the exhibition space. Through infrared-detection visitors force the computer to do sped up rebuild from scratch of one of the traces onto an empty map. After that the computer fills up the map again with all registered traces and the projection returns to the realtime situation in which all active participants can be followed live.