Update, Aug 2022: I've finally created a guide on how to make these. See this blog post for a full guide and much better maps!
A while back I read a cool article from the Washington Post, that showed how far a person could drive in one hour from the center of a city at different times. I was looking for a new apartment at the time and the spidery, heat-seeking pattern that followed the major highways and some smaller roads that I wouldn't have expected outside of Washington, DC inspired me to get some better data to find out where I should live.
I decided to make a map that would show me how long it takes to get to work from different locations around Philadelphia using public transit. I chose to start with mapping to City Hall, aiming for a nine am arrival time.
For a zoom-able version, click on the image or go here.
I like how each PATCO station in New Jersey is centered in a green splotch and the MFL and BSL are outlined in blue going in all four cardinal directions.
I also mapped one for a commute to the Navy Yard. This one is for an 8 am arrival time, since most Navy Yard employees get to work earlier.
The most noticeable difference is that its a lot harder to get to the Navy Yard than to get to Center City. The biggest challenge is that the BSL ends about a mile and a half before the Navy Yard, so if you want to use the BSL you have to add an extra 20 mins or so to take a local shuttle to your final destination.
There is an express shuttle that leaves from Old City, which results in the patch of green next to the "a" in Philadelphia. But because a transfer to the express bus is required, the effectiveness of the BSL and MFL is decreased. In this one, you can only see a slight green train going north-east following the north end of the MFL; there isn't much else effective.
If you work in Center City, you can live pretty much anywhere in Philadelphia and quite far into the western suburbs or New Jersey and still get to work in under thirty minutes. To achieve this goal if you work in the Navy Yard, you need to live very close to a SEPTA stop. Comparing the two commutes, you can generally add about 20-30 minutes to the commute time to Center City to account for the express shuttle to the Navy Yard.
To make these, I used the Google Maps Directions Matrix API to get the travel times for each coordinate. In this resolution, I had to map about 50,000 different coordinates and then drew a square around each of those coordinates into a geojson file.