i have sd card chips that give you added map views and auto guidance for Great Lakes region.https://www.ebay.com/itm/112553448893
Selling for 35 dollars shipped to your door.
i have it on my own boat and it works great.
person i got them from installed marine electronics for a living and believe it or not some people would just give him old units and cards.
cards still work on most new units. All units are identified in my eBay link.
this is a 300 dollar chip if bought new