Start in the USA. Leave by the westernmost crossable border (by foot or land vehicle) to a not-yet visited country: in case of a tie (due to tripoint) depart as close to westwards as possible. Repeat until you visit all connected countries. If there are no more connections, revert to the prior country.
All overseas borders count
Unbridged rivers *not* allowed—there are more of these than you might guess
Connections by bridge or tunnel *are* included. This adds a few islands!
If there is a border dispute, the borders according to the *current* country count
A couple mistakes that I found before the puzzle went live crept into the live version anyway: apologies. (I forgot Lebanon, for one.)
I'm happy to hear of other mistakes I've made, since odds are good there's at least one left. Random unfamous bits of border on an island are hopefully the most likely culprit.
A couple (maybe) surprising points:
1. There's very few bridges in the Guyanas
2. Unbridged portions of a border change the order of the quiz at least twice
3. The Netherlands, the UK, Finland, Sweden, and France all have relevant borders offshore.
I'm happy to hear of other mistakes I've made, since odds are good there's at least one left. Random unfamous bits of border on an island are hopefully the most likely culprit.
A couple (maybe) surprising points:
1. There's very few bridges in the Guyanas
2. Unbridged portions of a border change the order of the quiz at least twice
3. The Netherlands, the UK, Finland, Sweden, and France all have relevant borders offshore.