"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. The darker green areas have the greatest accessibility to jobs; the lighter green areas have the least. The red lines show transit routes."