rj'sjeep

I know these are grannie base maps does anyone know if it is possible to load their top maps into he factory system? or perhaps use a secondary device attached to the usb port on the 2015 models?

rj'sjeep

these are Garmin base maps not grannie ----- Spellcheck

Grand Umpah

I'm pretty sure that the answer is no; you can't upload maps into the 430n or use another GPS to input maps for display.
Best you can do is upload waypoints, either through the coordinates screen or as points of interest; the latter allows you to upload any number of waypoints in a csv file using a USB memory stick