I download a Garmin map online 2011 and I install directly to my Garmin 255W and it works fine.
I tried to update for my friend Garmin 250 but his interal device memory did not have enough space. Anyway he gave me his SD card SDHC 8GB I put the map on the SD. His garmin won't about to recognize it
But I tried to use it and view picture I able to see the picture working great too.
Yes, you can load the POI onto the SD card. I have tried this before. However, I find it inconvenient because I sometimes do change the SD card. The POIs are quite compact, it does not occupy much space. It is better to load them on the unit memory.
SD card are great for mp3 files. I have a nuvi 750 that only has 2G internal memory. That is barely enough for the maps. I use it as an mp3 player on long car trips. It automatically stop playing music and do GPS announcement at upcoming turns etc so there is no worry about music too loud and missing a voice prompt.
File structure for SD:
sd:garmingmapsupp.img << your maps...
sd:garmingmap3d.img << your 3D-buildings.... sd:garminJCVDddddddd.JCV << your junction view file which matches the map version
For additional maps:
You can create a folder called Map in the root and put the map file inside. The files in Map folder can be renamed as you wish and you can put more than one map in this folder.
Example: "X" is your Garmin driver
You can do the same in SD card
You can use the Garmin folder in SD but you can use only one map, named gmapsupp.img
How to name two different maps into the SD card so that the Gps Nuvi 350 can read?
I have create a folder name: garmin
then subfolder: gmapsupp.img for my first map. Now, the question is how I name my other maps that I have created.
I called Garmin since I installed a memory card and it didn't recognize it.
They said that it would use the card next time since there is still enough memory left.
Hopefully that is what will happen. I put in an 8 GB one and it should be enough.
I had only installed the lower 49 states,but I wanted the whole USA.
I hope this helps. If not call Garmin for support.