The main page is index.html, but most of the code is in map.js. map.js uses d3.js to render the map based on JSON data
generated by a couple Python scripts.
If you'd like to set this up yourself, you'll need to unzip the google_transit.zip file into this directory, then run
python3 generate_routes_json.py and python3 gtfs_json.py to generate the required subway.js and gtfs_json.js files.
These are required by virtual_rider.js, which implements Djiksta-like algorithm for simulating a rider's journey
from a starting stop throughout the system. virtual_rider.js is invoked by map.js whenever a stop is clicked,
and the results are used to shift the distance of each stop away from the clicked stop.