In both examples, concentric circles are a pretty good approximation. Considering that the 15-minute walk area will have high variability due to walking speed a

In both examples, concentric circles are a pretty good approximation. Considering that the 15-minute walk area will have high variability due to walking speed and traffic lights, detailed contours just give a false sense of accuracy. Like a bathroom scale that reports your weight to nine digits. Don't get me wrong, I love travel time maps in the right context. I actually made an interactive travel time map for transit in Toronto. It only works in Chrome but can be found here: http://ttcvis.s3-website-us-east-1.amazonaws.com/ http://ttcvis.s3-website-us-east-1.amazonaws.com/ Thanks for the link in the edit, I love write-ups of data visualizations and from a quick skim this looks really interesting.