@Ray-de-Jager In practice, you cannot upload any other base maps with underwater details (bathymetry, depth contours, etc.) to your Suunto Nautic other than those provided by Suunto, and there is no documented “unofficial” solution for importing Navionics, CMAP, Openseamap or other maps. The only option is to import GPX/KML tracks from external nautical tools, which the watch will display as routes on top of its own base maps.