@kevinvh
What's written in Post #28 is exactly what's meant, "processed" not "created" i.e. existing custom maps such as OpenSeaMaps are treated so they become usable in the device. You will need to search for GCCMapsPatch0.0.3 (which is short for 'Garmin Chartplotter's Custom Maps Patch Version 0.0.3') as it's not allowed here now due to changes to forum rules, some years back.