I can tell you that you can preview Navionics mapping on their web app. Here is the link to the Web App https://webapp.navionics.com/?lang=e...%7B%7CkoGfinxP, after you go the areas or lakes you fish click on the sonar icon lower left for the High Def SonarChart Layer. From there I would rec. the Navionics+ Preloaded, it is preloaded with the Nautical Chart layer for the entire US and Canada, you then add or download the high def SonarChart layer of the are you fish. You get a year of updates or the ability to refresh the card for a year so your card will not go out of date for the first year. After the first year you can renew the Freshest Data for another year for 50% of new.
Navionics+ is on sale right now Navionics Plus | Navionics
You can also log sonar and upload the logs to Navionics and they process the logs into the existing data making additions and possible corrections to mapping. You then refresh your card with new data so you can use it in your sonar.
Navionics Marine Specilaist