I fish exclusively small lakes with no mapping, and would like to start mapping these lakes. I am looking at the Helix 7 mega or equivalent Garmin 7" to map these lakes. So looking for input on either of these sonar units you might have used for creating your own maps. Really like the looks of the Hummingbird with auto-chart live. It is my understanding though that without a z-line card, I can not probably record more than one lake. Where as the Garmin just uses standard sd cards to map. Thoughts? Experience with either sonar?