The invention relates to a method of determining a location of a mobile device for use in a first communication network and a second communication network. The mobile device is camped on a cellular base station in the second communication network. According to the method, a list of records of communication units within the first and/or second communication network that are located within a predetermined geographical area is obtained. A communication unit record contains information representative of the identity of the respective communication unit, information representative of a position of the respective communication unit, and a reliability indication of the respective communication unit. Additionally, with the mobile device, communication units within the first and second communication network are detected. Finally, the location of the mobile device is detected based on the information representative of the position, the reliability indication, and an accuracy indication of the detected communication units.