Different country OSM unite in one.

Gretting. Is it possible and how, unite, for two or more different OSM (countries) in one file for Gpsmap device on micro SD card.
For example, to unite France and Spain in one OSM?! Thanks.

Copy the contents of the osm element from one file to the end of the osm element for the other. You may need to move bounds elements to the beginning of the osm element.

You assume that OP acquires osm extracts and runs mkgmap, we can’t tell for sure.

I recommend re-asking in the Garmin sub forum here.