During the last finals week of my junior year, an interesting website came online at density.adicu.com. It tracks the number of devices connected to WiFi access points at many places on campus, and translates these numbers into a crowdedness metric (100% := full, 0% := empty). The website, however, only shows the crowdedness at the instant you access it. ρ(t) is a tool I made while procrastinating during finals week that scrapes data from the website every 15 minutes and shows it using a D3 plot. It's not a smart solution now since there's an API, but it can show you how to scrape a website.
Above is what ρ(t) recorded during finals at Columbia. The largest fluctuations are between daytime and nighttime (although a fair number of people stay active at Butler, the 24-hour library). We can also see on most days a swell in activity after lunchtime. In my experience, finding a spot in the library was impossible just after lunch.
And we also see the beautiful, gradual death of finals week over three days.
If I were to remake this today, I would also probably use Chart.js:
Page created in January 2015.