What is GPX?

The GPS exchange format: tracks, routes and waypoints, as XML. It's what watches, bike computers and handheld units produce, and what hiking and cycling apps import. Fixed fields, no room for extras, works everywhere.

What is KMZ?

A zipped KML, sometimes with icons and images bundled alongside. It's what Google Earth hands you when you export, and it's a single attachment rather than a folder, which is most of the appeal.