TomTom and Garmin both produce GPS devices that produce often very similar navigation instructions, they differ when it comes to file compatibility. Many TomTom map set files are formatted in OV2 or OVR. Garmin GPS devices can’t read this format. Garmin map set files are typically formatted in GPX. If you have purchased TomTom maps and now wish to download them to a Garmin GPS, the files need to be reformatted. TomTom map set files can be converted to a compatible format using a software program or online conversion tools.