I am a Humminbird fan and also I like the Navionics sonar charts. The charts are done by fisherman who record when they are scanning, then those recordings are uploaded to bird and they up grade maps. Anyone who has the right chip can update and download the charts. They are very detailed.
So I just purchased the Navionics + sd card. It allows me to download what maps I want up to 2gigs. these maps are anywhere in USA and Canada. I made two downloads.
1st. all Indiana, Kentucky, western lake Erie, eastern Wisconsin up to and include green bay.
2nd. Kenora canada up to big sand lake.
Total download was about 1 gigabyte. I have a year I can update whenever I want.
I think it is a swell product, download only the maps you want. cost is about $175