Nice work! Just a curiosity question: Are you downloading your GPX in their reduced form or are you reducing them outside of Observable?

Glad you like it! The original GPX files, whether they come from my Garmin GPS watch or my iPhone, tend to be quite large. They actually work just fine in the notebook, when I run from my machine but I still figured it would be a good idea to reduce them, which I did using https://gpx.studio/.