how is cold-potato done?

[Ralph Doncaster <ralph () istop com>]

If I peer with network X in cities A and B, and receive the same route in
both cities with an AS-path of X, how do I know which city to use for an
exit?  I can understand how if X uses communities to tag the geographic
origin of the traffic, but I'm not aware of many networks that do
this.  Lots of networks claim to use cold-potato routing though, so how do
they do it?

Ralph Doncaster
principal, IStop.com