Sonar/Chartplotter advice. Is this the right place? in GPS Posted September 18, 2009 MajBach, Had a chance to wade through Garmin's lineup of chartplotters and got a little closer to your questions. I just looked randomly at several models, including the 4208, and they all seem to use the same approach...YMMV. Maps, waypoints, and tracks are transferred to/from the GPS via an SD card (unless you or someone can figure out NMEA). That is, copy data from the GPS to a card, move the card to a computer, copy from the card; and vice-versa. I didn't see any that use a direct computer connection such as USB. So, yes, given a large enough SD card, you could transfer your map, track, and waypoint data from a computer to the plotter...up to the memory limit of the plotter. Unless someone can clarify NMEA for you, a whopping big SD card should do the trick. Can't help you with the transducer stuff, our water is shallow enough that it never gets to be an issue. Cheers! Thanks for that input. I actually went the old fashioned route and called Garmin (after hours on-line searching). Spoke to someone right away and learned that NONE of my maps on CD will work in ANY Garmin marine unit. They must be Bluechart V2. Not even navionics works. Hello Lowrance! Just when they were about to take over the market (I was a die-hard Lowrance user - handheld and marine until Garmin made mapping so versatile and I bought a 76 CDx), they go and do something selfish and arrogant to put their competitors back on the map. If I am going to have to buy new maps, I am going with Lowrance. They did say I could use my waypoints etc from the 76 onto the marine unit though.