I days long past each of the mapsource tiles was actually the data contained in .IMG files that mapsource used as it's input files. Garmin later changed a lot of things and one of them is the replacement of those .IMG files with a new format and named .GMP files which are scatterd in a bunch of tile folders in sub-directories/folders of the .GMAP folder/directories. The .GMAP folder is a top level folder of a directory structure which contains EVERYTHING you need to install maps in mapsource. Note that Mapsource still works with the old style IMG files, they are just more difficult to install and manage.
When mapsource starts it looks for that .GMAP directory and if it finds it your maps will be loaded (if they have been unlocked). By defauly Mapsource looks for that .GMAP directory in different places based on the Windows O/S you are running.
The default locations for the GMAP top level folder...For XP
C:\Documents and Settings\All Users\Application Data\GARMIN\Maps
For Vista or Windows 7
C:\Users\username\AppData\Roaming\Garmin\Maps
Here's an example showing where North America is located "by default"
For XP
C:\Documents and Settings\All Users\Application Data\GARMIN\Maps\City Navigator North America NT 2012.30.gmap
For Vista or Windows 7
C:\Users\username\AppData\Roaming\Garmin\Maps\City Navigator North America NT 2012.30.gmap
There's one little twist... Suppose you want to put those large map mapsource installations on a drive othere than "C". That is very easy, that top level .gmap folder can go anywhere you like. All you need to do is create a link/shortcut to the real location of the .gmap folder and place that shortcut in the appropriate default directory on your "C" drive.
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