href="activity.html#fig:nightcrawl">6.6</a>, in which all data points are plotted that were registered by the smartphone of person 2 between 02:00 and 06:00, At those hours, the person was sleeping, in the bedroom of his house. He did not move. Yet, if we would take the GPS-data for granted, he regularly took a nightly random walk in the park. The red dot in the figure marks the median coordinate. This coordinate is very accurate: it marks the bedroom. All individual data points, however, fail to identify t