You can connect your Garmin GPS in USB mass storage mode and show the map in BaseCamp or you can use a USB-stick or a memory card. All are USB mass storage mode devices.
The GarminDevice.xml file in your Garmin unit gives clues to where different map files and additional files should be stored. BaseCamp should anyway always be able to read "[USB-stick or USB connected Memory Card]:\Garmin\any_file_name.img" (example "X:\Garmin\Gotalandv3.img" where X is the drive letter for a USB mass storage mode device.).Code:Please Login or Register to see the links
External HDs are not inside the Garmin scope of USB mass storage mode devices. Try this tool if you want a virtual SD card residing on your hard drive: [Only registered and activated users can see links. ]