Navionics now has the ability to upload sonar tracks that have been stored to your Lowrance Chart Plotter from the day you started using your unit and use this to improve mapping via the Sonar Charts program.

Lowrance and Simrad models automatically store sonar data by default during everyday use, so unless it was turned off, there is a whole library of sonar logs residing on the plotter’s memory since day one. All you have to do now is export from the chartplotter to an SD card and upload to our website. Once sonar logs are saved on a card, it can be plugged into a computer and the data is transferred to Navionics through the internet to generate new SonarCharts™ for all boaters in about one week. Boaters can choose to share all of their logs at once or they can record and export specific files.

Check out how: http://www.navionics.com/en/plotter-tutorial/lowrance.
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