Here's the author's source code: https://github.com/chriswhong/nyc-subway-isochrones https://github.com/chriswhong/nyc-subway-isochrones If they were using the

Here's the author's source code: https://github.com/chriswhong/nyc-subway-isochrones https://github.com/chriswhong/nyc-subway-isochrones If they were using the Isochrone API, the buffers around the subway stations would take in account the street grid vs a circle. That's really cool that Mapbox now offers an API to do this. It seems like it also factors in elevation as well!