Classroom Seating Habits

This from Flowing Data:

We all have our seating pockets that we like to settle in. Skyrill, a two-brother design team, took it upon themselves to visualize the seating habits of their graduate student classmates in class 15.514 at MIT.

While you don't know the class or the students, it's easy to pretend that you do. Select students, find who likes to sit in the front all the time (Dario), who likes to sit in the back (Arthur), and who jumps around a lot (Takumi). It looks like the room entrance is on the left since people sit there more often. You can also play it out and watch each student move around the class.

Next step: provide more context. Why is the seat in the front, third from the right always empty?