@axxxtw
In addition to and in clarification of the above reply: It's helpful if we know the unit model you're using. Some Nuvis handle 2 maps in Garmin folder of sd card (with recent fw), as gmapsupp.img and gmapsup1 img (eg 2xx, 7xx). Some only handle gmapsupp.img in Garmin folder. Modern Nuvi (eg 1xxx, 2xxx, 3xxx, 30/40/50 series) can handle multiple maps with 'anyname'.img in a folder named Map in root of either unit or sd.