I have both a 1400 and a 760, On both units I run the topo (two sets) maps from a SD card. From memory when I set the 760 up there was not enough space and I just followed the same structure with the 1400, Wanted to leave room on the device for POI and other files.
I have just finished a long session on the phone with Garmin support to correct problems with my 3790T. The conclusion was that I should remove the SD card entirely and do a reset [view map, tap "speed", hold down "speedometer dial" then wait ... wait ... (maps did not disappear). Reload POI, Routes, Waypoints etc.
Original problem was that routes & waypoints were being saved to SD card but device ONLY looks in internal memory. Take it for what its worth.
I dont doubt for a second that you can use the SD for maps, routes etc. But I cannot find any way to tell my Garmin 3790 that it should look on the SD card for data. I am also puzzled why the Garmin support told me to discard the SD card because the 3790 doesn't use it. It all makes me think that maybe the 3790 is different??
What is the best location to have your data?
Is it on the Garmin or SD card?
I would prefer a 4GB MMC card
Don't ungerstand why you would rather put your maps and POI's on a data card rather than in the GPS unit where it has faster access to it.
Put your music / photo's and other useless info on the card and let the GPS have faster access to what it is there for, directing you to a destination.
Can you use a memory card with the custom poi on it in another Garmin GPS
Good idea, but, after putting some photos on a card in the new 3590, they were very slow to display, so think it may be better to instal to internal memory. 4gig cards are only a few dollars these days so I use separate cards for each GPS.