Micro SD card file format for 1490T

I am posting the following information so that it may benefit anyone that may need to organize their map data on a MicroSD card. This information was based on trial and error in addition to posts from this and other GPS user group sites. I do not claim to understand or know about any established or "official" file structure rules, but can attest that the following does work with my 1490T.

I have left the original files on the internal memory of the unit as they are, including an older version of the North America maps and .JCV files. Everything below exists only on the MicroSD card.

.System
LEX_PKG (various language guide files here)
GARMIN
JCV
xxxxxxxxx.JCV (.JCV file for NA map)
yyyyyyyyy.JCV (.JCV file for foreign map)
LEX_PKG (duplicate of .System/LEX_PKG files)
POI (empty, but poi files might work here)
gmapsupp.img (this is a foreign country map image)
gmapsupp.unl (this is file with 3 unlock codes)
zzzzzz.gpi (there are multiple different.gpi files)
MAP
xxxxxxNA.img (renamed NA.img file -
however, it can also be named
gmapsupp.img)

I also have another folder titled MYBACKUP where I have .txt files with instructions, backup copies of some of the files, etc.

The unit does not seem to care that the MYBACKUP folder is on the SD card.

The gmapsupp.unl (text)file has three 25 character unlock codes, each 25 character code run together with no spaces and in the following order: Lang Guide, Foreign Map, North American Map. I have no idea why it needs to be in this order for me, but through trial and error, it was the only order that would work. Any change in order of the codes would cause one or more of the maps or language guide to not load.

I was able to swap the location of the foreign language .img and the NA .img, but whichever one is in the GARMIN root folder HAD to be named gmapsupp.img. The one in the MAP folder can be renamed to whatever you want.img or it can also keep the gmapsupp.img name.

When booting the unit with this SD card, it gives a message "loading maps" then has a screen asking if I want to load the card data to the internal memory. I always decline.

In the tools/settings/map/info menu screen on the unit, it displays both maps, each with a checkmark box that you can toggle on/off.

In the past, the language guide would work with the 2 maps installed, but now gives an error that it is not installed, even though the files are present on the SD card. I suspect that as I have updated new versions of maps, I may need to juggle the order of the unlock codes to get an order that loads both maps AND the Language guide. It masy also be because I have duplicate copies of the language guide on the card. I rarely use it and don't recall why I have it twice. I recall seeing somewhere that the unit expects to see the order of the unlock codes based on the numerical "sort order" of the .img files. No idea if this is true or not and will update if I find out a solution.

If I boot without the SD card in the unit, it will load the original (obsolete) map and .JCV file and will work fine, albeit with old data. (It will also complain that I have not updated the maps)

As stated above, I am only posting this in case someone else is struggling with a similar need for having multiple maps on an SD card. I have no idea if anything I have posted will work on other units, or how one would load more than 3 mapsets on a card.

If anyone knows what the "official rules" are for how the file structure works on an SD card and the intricate pecking order of the file order, I would love to know what they are.