brettw, you can get reefmasters to make the maps of your lake but you can also get the mosaic and bottom composition module. The first is shown above and the other will take the reading to make a map of bottom hardness / composition on your lake. Not using it due to the feature of red / green on the HB. By using it I was able to find points this summer that held some big gills. Several point were checked but only the ones that had the hard bottom returns / pea gravel were holding the big gill.

Some of the guys on their site are doing way more and better jobs than what I could hope to do....but fun trying

You can get reefmasters as a free trial and see if it is something you would like. Hit Matt up, he is more than willing to help in any way I've found...great guy.