To update maps for your garmin, we need to understand the file structure.
Device Memory.
The maps  installed in your device will be in .System folder. This folder are hidden, unhide.. look here
The maps file are with .img extension and usually the files listed as below.
                gmapprom.img – factory preloaded map.
                gmapprom1.img – another preloaded map (if any)
                gmapsupp.img – supplementary maps ( i.e. loaded from mapsource)
                gmapprom.unl – unlock code for gmapprom.img
                gmapprom1.unl – unlock code for gmapprom1.img
                gmapsupp.unl – unlock code for gmapsupp.img
                gmap3d.img – 3D Buildings map
                gmap3d1.img – Secondary 3D Buildings map
                gmapbmap.img – garmin basemap
                gmaptz.img – Garmin time zone map 
                gmapoem.img – OEM mapset
so if you want to add new maps to device memory use one of them. 
The junction view file will be in  .System/JCV folder.
SD Card 
Map on SD card must be placed inside Map folder. 
Interestingly the name can be any name i.e. Gcc2010.img 
You can install as many maps as possible as long as it not exceed your SD card size and each map not exceed 4GB.
The junction view file will be in  garmin/JCV/ folder.
 
