Isochrone
An isochrone is an isoline for travel time, that is a curve of equal travel time. Closely related is isodistance, which is a curve of equal travel distance. Typically these are based upon following transportation routes such as public transit, roadways, or foot paths rather than using a simple circle (a.k.a. buffer of a point, "as the crow flies" distance). This article will use the term isochrones, however any weighting factor can be used such as distance, or even a combination such as safety and time.
