Indeed, you can't do this perfectly – it's an approximation. I just use one of the two directions as the travel time because if I wanted to symmetrize I'd have

Indeed, you can't do this perfectly – it's an approximation. I just use one of the two directions as the travel time because if I wanted to symmetrize I'd have to call the Google Maps API twice . Asymmetry aside, it's also not possible to perfectly embed metrics in 2D Euclidean space, or any-dimensional Euclidean space for that matter (see other comment)