Mapnificent
A new web site called Mapnificent lets you see how far you can travel by public transportation in a certain amount of time. Simply drag the pin and move the time slider. I made a quick animation above showing 15-30 minutes from my home; Boston, Cambridge, and Somerville are easily accessible. This also illustrates a point that I’ve always made: the Charles River is a big divider, most places are more like ovals stretched in and out toward boston, and not a short distance north and south.