ok I have sold my Ranger 620 and Alumacraft Competitor 165 Tiller I am going all in on a tiller. My choice is a Ranger 618t I want to change from Lowrance HD units to Hummingbirds Onix Series so I can link them to my Minnkota Ulterra that I also ordering. My biggest concern is being able to find a good Topo map for my lake in Canada O'Sullivan Lake near Nakina. I realize that it's not a mapped lake but I had found a really clear topo map made for my old Lowrance unit made by Trakmaps showed every island in great detail. Does anyone have an idea on how I can have really have good topo details with my new hummingbird unit. I have heard that the basic mapping has some details but have not seen it. How about an sd card that works?