from the site:
It looks a bit like an isochrone, a map showing how far you can travel on a transportation network in a given time frame, starting from a single location.
But this map tells us something about every point of origin in the Minneapolis/St. Paul region simultaneously. Specifically, it tells us how many jobs are accessible within 30 minutes - using the key at right - from each location by public transit, during the 7-9 a.m. peak morning window.