As you may see, the most significant drawbacks of JNX format are locking to a device, and impossibility to make a JNX file from some existing raster map you have. Besides from JNX and KMZ, the raster maps in Garmin GPS can also be in IMG format. See more here (only in Russian at this moment). Results of the research The JNX format is almost completely reseached (except for the parts of map loader