I have the 598Si, and a Navionics map chip. If you but the Navionics app on the app store for a phone you can take a look at the maps, they are exactly the same. There are a few lakes that have decent contours but most are the government maps that were done in the 60's. The 598 and 798 are virtually identical except the 798 has 2 sd card slots, ethernet for connecting to other fishfinders and 3 programmable hot keys. Using the side scan i found a sunken boat on hackett lake which was quite neat, didn't get a screen shot. I also had an accident with my net and was able to see that on the bottom as well. If you have any more questions let me know. I've only had it out for 1 weekend but was quite impressed with it.