## 4 Case Study Description
### Characteristics of GPS Traces  
TU Delft has been developing a crowd monitoring system for some time. The input of this CMS is very diverse, ranging from automatic counting data to GPS traces. Mysteryland is one of the (music) events which are used to test new data sources, data fusion algorithms and forecasting algorithms. In previous years, the use of GPS traces as an input to the CMS has been studied by [6] and [7], but deemed too labour intensive to be a viable data source for the CMS. However, a smartphone application of Woov opened up a different, less labour intensive, way to gather GPS traces in real-time. The aim of the joint project between TU Delft and Woov at Mysteryland was to determine whether the GPS traces gathered by the smartphone application of Woov had enough explanatory power to be used for the real-time monitoring and online forecasting of crowd movements at large-scale events.  
The company Woov has built a smartphone application for the Mysteryland event which informs its users regarding the programming, the upcoming events and location of facilities (e.g., toilets, food, first aid) on the terrain. More importantly, this application allows its users to determine the current location of their friends on the terrain and provides the users all essential information to find their friends. Friends are, according to the definition of Woov, individuals that granted another specific person access to their location-information for the duration of the event within the region where the event takes place. In order to provide location information regarding a friends' location, the smartphone application records the GPS locations of all individuals that use this app (with their consent) and some characteristics of each person (e.g., age, gender, network of friends). The application of Woov asks the location of all smartphones connected to their application, which they impersonalize and save in their database for short-term usage. The GPS data consists of latitude, longitude, timestamp, accuracy, id number of the person, age and gender. The services provided by the application (i.e., finding friends, getting information regarding facilities at the terrain and receiving instructions from the event organiser in real-time) are the only incentives that users get for providing their location information and socio-demographic information. The terms of use of the smartphone application details what the company Woov is allowed to do with the data provided by the users. By accepting the terms of use, the users accepts that their location information is used for several purposes.  
Only the anonymized GPS data, and some metadata thereof, were shared with TU Delft, as a part of a joint project after the unfolding of the event. Each person in the shared GPS data is identified by an id number. Consequently, the researchers do not know to whom a certain trace belongs. The location-information of all users of the application is used in this research.  
The dataset of Woov captured location data on 9,748 distinct individuals at Mysteryland. After filtering (see the following section for the details), 13,461 continuous trajectories. As the GPS position is determined using a number of complex algorithms, the accuracy of the measurements is reasonably high (i.e., \(\pm 10\) m).