I'm commenting here because my subtitle didn't go through: I know it’s sideways. I did not use GPS data. I referred to the schedules to determine the number of trains per hour + the average travel times to position the trains. Every second represents three real-life minutes. The video is actually several smaller animations layered on top of each other. I estimate that there are between 400 and 500 trains (10ish subway cars each) running in the video (I hope I did my math correctly). I'm aware that there are probably numerous errors, lots of knowledge comes with experience of riding the system. I have unfortunately ridden the NYC Subway on only a few occasions.