sonar/gps question

I was planning to get a new sonar only unit, but now am considering a sonar/gps combination. I have never seen one in use and was wondering if there was a website that had a simulator that showed how the Navionics or a similar type of mapping system works. Thanks.

humminbird.com

lowrance has an emulator you can download and play with all the buttons on gps,but as far as the navionics card. thats just a detailed background map. all the features are done by the gps unit not the card...hope this helps