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Comment by puzzledobserver | Hacker News Reader

This sounds conceptually difficult: Wouldn't the presence of one-way streets or airport security checkpoints, for example, mean that the travel time from A to B might not be the same as the travel time from B to A?

How can a map then be drawn?

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Right. There could be northbound traffic but not southbound for example. The answer is they must be symmetrizing the distances somehow. Alternatively, you could show the travel times _from a source location_ unambiguously, which might be more interesting for the average user (e.g. from home)

Yeah, this is what I was hoping for with the touch. Seems like where I touch should be the origin and distance in x/y should represent time to travel from that origin.

That still wouldn’t work in all cases. For instance if a ring of locations are all more accessible than a location they contain. Which applies to basically all suburbs.

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)

Before trying the site I assumed the way they would resolve this is that the distance calculations would be made relative to the point at which you held the map, but what actually happens is that the map is drawn uniformly no matter where you hold it. and of course this is an impossible representation due to the reasons you describe as well as the differences in mappings between a path that is configured to be walked in one direction, but traveled by vehicle in the other.

Good point.

And hills are rather easier in one direction too.

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