If using Windows, plug it into your computer and it should be recognised as another drive. You can then see the directory structure of the GPS.
Just be careful you do not delete anything as the GPS will fail if removing a system file.
Thank you for your reply, i still can't find my main map.
It depends on how your computer program (windows explorer) is set up.
The default is to NOT show system files, and this may also stop you seeing the main map as is could be recognised as a system file, as the GPS wont operate without one.
Unless you know what you are doing, and getting into any system file area, you could make your computer in-operable with even the smallest deletion, so will not say how to change the settings.
Not sure, but suspect it uses both, as there is a huge amount of info in the mapping files.
I personally wouldn't try to open any of them as they are not a file you should be attempting to modify unless you really know what you are doing, and think you would need the program that set the mapping up, to be able to safely edit anything.
If you want to use a Macintosh to see the file structure on a Garmin unit, you will need to make the System files that are normally invisible (file and folder names that start with a '.' in the file name will be invisible). Use a free tool called 'Tinkertool' to temporarily make invisible files visible in the Finder. You can search for 'Tinkertool' to find the latest version. Like the cautionary notes offered by others, don't change files unless you know what you are doing.
If you make invisible files visible, you can then copy all of the files from the Garmin unit to your computer so as to make a backup of the GPS unit. I always do this before performing any updates of GPS maps or software. It has saved me from bricking the device a couple of times already!
If you are going to show hidden system files I recommend you do what ever it is you want to do with your sat/nav, then change the folders view option back to hide system files and, like aspeel says, do a back up of your gps unit 1st...
The 1490 does not have enough room in its memory for the latest map updates so it places them on the micro-sd card which if you look on your directories should show up as a separate drive letter. The map is in the folder Garmin.
The general map with little detail is in the Garmin itself.
I suspect the main map file is located in the \.system folder and is called gmapprom.img. Updates probably take the format gmapsup.img Logic suggests the sup stands for supplimentary and that you still need the origional gmapprom.img file installed. If you temporarily change the suffix (extension) of the gmapprom.img file to say gmapprom.imz the map will not appear when you check the maps installed in your device. If you try this, don't forget to change it of course.