We divided NYC into 2,930 hexagons and calculated the time it would take to travel by subway and walking from the center of each hexagon to every other one using OpenTripPlanner and the MTA's subway schedule data. We simulated each trip as starting at 9 a.m. on a weekday.

The 4,290,985 calculations took four extra-large Amazon Elastic Compute Cloud instances just under a week to complete.

We generated the hexagon grid in the open-source mapping program Quantum GIS using the MMQGIS plug-in. Here's that grid as a shapefile and as TopoJSON. And here's the 33MB zip file with each hexagon's data as json.