Umm... i'm unsure but i think these chartplotters are designed to simply accept pre-programmed data cards with a single image, but you can of course combine charts/maps as a single gmapsupp.img as you described for SD card, and other than the OEM pre-loaded map nothing in the way of maps/charts can go in the internal memory. But i'm a 'nuvi boy', not really a boatie. If no one else replies to the contrary, how about you have play-around when you get it to see what it can recognise and then let us know what it'll do?