Navionics has charts online at WebaApp | Navionics
They offer the standard charts, plus their new SonarCharts. SonarCharts are turned on when in the web application via the little sonar icon in the lower left corner.
I'm surprised at the differences, turning the sonar on and off. I had thought they wouldn't have advanced sonar everywhere and provide the more detailed information by doing an interpolation between the NOAA chart depth lines. When I look in lots of little places it's clear that they are not doing that.
Does anyone know which depths are more accurate? I'd invite people to explore areas that they know intimately and report on how the Navionics data relates.
I've heard that Navionics is going all "social media" on this. Users are encouraged to go online with their cards and refresh to newer charts and chart notes. Their new memory cards can record user notes and will collect depth data, which is shared and combined with other data every time they go on line. That means every fisherman trolling is actually doing data collection for our charts. Pretty interesting. You can leave chart notes that there's a really bad bottom at your favorite anchorage. If everyone uses the system you could depopulate an anchorage by giving it a bad review.