Can someone point me in the right direction to update the stock maps on a Lowrance LMS-339 unit? The unit will accept 1GB SD cards and it seems I should be able to install new maps that can be downloaded from this site.
Map formats are proprietary and will only work on the manufacturer's own devices. All the maps on this site are in Garmin's format and only compatible with Garmin devices. So, unfortunately you will not be able to use them on your Lowrance GPS.
A couple years ago I played around with Lowrance's format and started a thread here to see if others were interested in making Lowrance maps. Nobody was, so I moved on to other things. :)