You need to download the High Definition SonarChart layer to the card, the data that comes on the card is the base or Gold level mapping. The SonarChart layer is the mapping layer that Navionics updates when new mapping data is available the dynamic layer. Then every month or so you can update the SonarChart layer buy what is call the Freshest Data program.
Here are some examples of the St Croix. You can view all of Navionics mapping online on the Navionics website on the web app they give you both views click on the sonar icon lower left