For a while there I was pretty obsessed with data visualization. Below is output from a Processing
sketch that visualizes iPhone location logs from crowdflow.net
(A few years ago, there was a bit of a scandal about Apple secretly tracking the locations of its devices, presumably to optimize connectivity. Crowdflow was a lil' site where people could upload their location logs. The site scrubs identifiable information from the shared collection.)
Because the data is scrubeed, one can't trace the trajectories of people through the cities they live in, which would have been immensely interesting.