The origin of this map is described in slightly more detail in the original blog post.Errata / Disclaimer
Everything is an estimate. Rounding errors abound. Don't use this for anything but entertainment and curiosity. But you already know that.
Travel times to areas close to the coasts are prone to large errors. This is
because travel times are calculated and interpolated on a grid. Points in the
water are heavily penalized so if a city lies between points sampled on land
and water, the interpolated time may be extraordinarily large. Thanks to @ChristianTanner for
pointing this out for the very stark example of Dublin, where it appears that
it takes 14 hours to travel from Dublin to Dublin.
Some data may be missing. There may be faster connections.
If you find issues, please let me know
and I'll do my best to fix them.
Thanks to cuicuit on reddit and
@yorksranter for pointing out missing data
for Paris and London!
Ireland and parts of Spain are not well represented due to missing data.