via Flickr / roeyahram
There is something poignant about the straightforwardly named New York City Subway Turnstile Data Animation. Using public data gathered during the week of April 14 - April 20, 2013, Chris Whong visualizes the relentless comings and goings of thousands of faceless commuters--each green dot here represents 50 people entering a train station; red dots for the same number of folks exiting stations.
As is typically the case, the crunch wasn't as elegant as the reveal. As Whong explains, there isn't an aggregate number "of entries and exits for each station." Some stations have multiple turnstiles churning at multiple intervals. A majority of the data runs 4-hour interval counts, only these are offset between certain stations. And "some outliers," Whong adds, "do not seem to follow the same conventions":
Data for a specific turnstile for a specific time period is pulled into the map as the visualization runs. The number of entries/exits is divided by 50 and each group of 50 will be represented by a dot. To make the motions more fluid, a start and end time are picked at random from the associated time period for that data, which is used to display and animate the dot.