@mbajing_deh
I may have confused you with this statement:
.... use MapInstall to load your second map as gmapsupp.img from a PC version [gmap folder] or use SendMap20 to load an already complied image file.
Navigasi is not loaded to the PC as a more modern 'gmap folder' type of PC Install, it's an 'older style' PC Install version formerly known only as a 'Mapsource [Install] Version' and both installed types are often still referred to today as that or BaseCamp Install/Version. However via MapSource or MapInstall both types are compiled into an image file meant for use directly on the device.

You cannot use SendMap20 to deal with PC Install versions. It's function is to load a previously fully compiled image file directly to the device as a secondary detail map [gmapsupp.img]. This is of particular use with older devices such as SP 2720 which do not allow files to be simply copied to the internal file system the way modern devices do. SendMap can also delete a secondary map from your 2720 to create more space for a larger primary map [gmapprom.img] to be then loaded using Garmin's map downloading software, i.e. GarminExpress or MapUpdater, or the command prompt method described on Page 1 here for 'unlocked' maps.

What's initially quite confusing to newer users is that the maps installed on the PC such as Navigasi have numerous *.img files contained in them. If you compare the file names of these with the 'map tile' names in the fully complied gmapsupp.img you will see that the names are the same. Open your Navigavi gmapsupp.img in GMAPTool, press 'Details' and you'll see what i mean.

This should no longer be confusing to you at all, after you read the Tutorials link proved by catymag.