After that it dashed my hopes and popped up a message saying the map wasn't compatible with my navigation system. I hooked up the external HDD to the Uconnect usb port and the nav spent about 5 minutes 'Validating Update'. In the base directory of my external HDD I created a folder named Garmin and included the gmapprom.img and a gmapprom.unl file with appropriate 25 digit code based off my unit id and map id (created using the powers of the internet). I changed the name of my gmapsupp.img file to gmapprom.img. The RB5 unit does not default to contain Hawaii and that is where I believe my problem lies. The resolution on the gps was as high as on the pc, so at least for not so large areas it is an option.I preface the following with I tried loaded Garmin's 2013 City Navigator maps of the lower 48 and Hawaii onto the Unconnect. Used it this week to put a aerial image with some polygon overlays for a few hundred hectars onto a garmin. I think it depends on the area you are exporting what the outcome resoultion will look like (1 megapixel per tile times max. It will take quite long but will save a kmz that you copy into your CustomMaps folder (not sure about the garmin restrictions here about multiple custom maps and tile limit, so best try with only one kmz first). Start the tool from the toolbox (in the catalog where you downloaded it to) and put the 90 or something in the tilenumber. Just put your topomap into arcmap and zoom to the extent needed. Maybe that was why it did not work for you earlier. That are 1024x1024 Pixels and max 100 tiles in a kmz(some models can do more, but this is not documented but tested). The advantage of this toolbox (beside nothing necessary to install, free and a interesting python script) is that it honors the garmin built in restrictions. kmz that is also readable by your GPS (the garmin webpage tells that your GPS should be able to). Its a toolbox with a python script that exports what you are seeing on your active data frame to a.

There is a tool where you can export your active dataframe as a garmin custom map.

Garmin custom maps download