it appears Garmin considers their chart plotters a closed system. I had briefly considered using them in my electronics refit (new radar, new transponders, new MFDs) but am happy I didn't now. On Garmin I guess you get Garmin charts. On the e series Raymarine: NOAA raster, NOAA vector, CHS raster, Navionics in several versions, and now C-Map in several versions.

http://www.panbo.com/archives/2015/03/the_navionics_sonarcharts_for_garmin_conflict_messy_business.html