Fig. 2.

The probability that two Flickr users have formed a social contact on the site, as a function of the number of times they have taken pictures at approximately the same place and time. A shows the probabilities for a spatial cell size of s = 0.001° (or around 80 meters in the middle latitudes) for time periods ranging from a day to a year. The lower plot is the same as the upper plot but with a log scale on the y-axis. Also shown are plots for cell size s equal to (B) 0.01°, (C) 0.1°, (D) 1.0°, and (E) 10.0°.