Like most other maps, they are based on OSM data. When you download a certain country or region, the zip file will contain a map.img file and a contour.img file. Just copy both to your device and they will show up as two different maps you can enable or disable. Both enabled gives you the topo map with contour lines as an overlay.
How to convert Google My Map KML to GPX or Strava RouteBackground:A client recently sent me the routes that they had created on Google My Maps for a bike tou
Most companies have a software that allows you to transfer .gpx direct or convert to the native format of the plotter. In my case it is Humminbird PC. Garmin also has one called Garmin Express etc. The route should now be accessible. Google Earth: If you do not use the Navionics app you can accomplish the same thing with Google Earth directly. Steps to Generate GPX File of Your Route Map. 1. First, go to Google Maps website on your computer and plan your route. 2. To create route data, choose your starting point and destination on Google Maps. Click Options to make changes in the route preferences. Create a route data in Google Maps. 3. 2Wppam.