The integration of GPS-devices with handheld cell phones or small computers opens new perspectives for urban and regional research. Detailed knowledge may now be gained on peoples itineraries through the urban landscape, how places are embedded in use contexts with each others and how temporal rythms affects the different parts of the city. GPS-based tracking has previously mainly been used to track vehicle movements, fx. in transportation surveys. The use of personal devices makes it foremost possible to place the individual respondents use of urban space in its context of transport routes, other locations visited and the individuals total time budget. In the cross-disciplinary research project Space – Time – Flows currently being started at Aalborg University, the GPS/electronic diary technology is intended as a means to disclosure the imprint of information and communication technologies on the use of urban space. The core of the work will be an equal treatment of activities in the virtual as well as the physical world. Substitution effects between the virtual and the physical world will be in focus, together with differences between the spatio-temporal patterns of groups with different attachments and investments in the “virtual lifescape”. This paper is a part of the ongoing work towards GPS-based activity surveys. It addresses the problems with GPS-precision in dense urban areas and it presents the possibilities in GPS-based tracking of individuals. Analysis of itineraries and spatio-temporal activity patterns is presented based on sample data from the Greater Copenhagen area in Denmark. This is followed by a status of the work with the combination of GPS-based tracking and a suitable electronic personal/handheld activity diary. International Conference for Integrating Urban Knowledge & Practice Gothenburg, Sweden. May 29 – June 3, 2005