Is there a FAQ where I might find recommendations on which GPS / sonar combo to buy? I'm looking to map a lake and am most interested in depths up to 12 feet. I'd also like to thoroughly map areas around shoals.

The other main question I have concerns whether the GPS/Sonar combo can only be used to provide a depth reading at one point at a time or whether this software can use additional sonar image information?

Any pointers would be greatly appreciated.

Recommendations on what combo-unit to buy is like asking people what car they like. Lowrance/Simrad/Humminbird/Garmin and Raymarine alle have units that can be used to do the actual collection of data. (Often referred to as "logging".)

The units that are by far the easiest to make good looking maps for are Lowrance and Simrad since Navico (who owns both) have been kind enough to publish a tool to transform maps from Reefmaster into maps that work very well on their units. The same sort of stunning maps can be made for Garmin, although it is a more tedious process. Reefmaster can export in a format for Humminbird, but the format is pretty simple. For Raymarine there are no good ways to make maps, and after mailing with them I doubt there will be.

So the cheapest combounit that you can also make good looking maps for is Lowrance Elite HDI, both the 4,5 and 7. From there on personal prefference makes a big difference, you will probably find that a lot of users on this forum preferr Lowrance HDS since there are more options for maps in those units then in the more budget-friendly Elite HDI

All Lowrance and Simrad combounits records sonarlogs wich is what you will use for making your maps, they contain both depth and position, but also the full sonarhistory (what you see on your sonar in your boat) and Reefmaster shows this history like a playback. Garmin has a similar function on some models, but without position, so it's harder to use the sonarlog to check and study the logfile from Garmin.

I should add that I'm ProStaff for the Norwegian importer of both Lowrance and Simrad, but that does not make any of what I just posted less true. ;)

Well said Team Colibri. I totally agree with you!
Especially if you want to use the map on your chartplotter or combo unit.

Thanks for the info on combo units - I'll go off and research the units you suggest.

I'm still a bit confused about whether the information in the sonarlogs can be used to create contour (bathygraphic?) maps of the lake bottom, or whether you can only use the depth reading directly below for each GPS point.

Steve,

Only depth below the boat is used for bathymetry, but other data in the sonar logs is used for other things, including bottom composition and sidescan mosaicing. I assume you are talking about gathering extra depth information from sidescan? Technically, this isn't really possible. There isn't any extra depth information in those channels.

Matt

Screenshots from my own Lowrance HDS 8. Data collected with Lowrance-units and maps made with Reefmaster:

I have own a Lowrance Elite 4HDI as well as the more expensive HDS5, both are good units and suitable for mapping. My only complaint with the Elite unit is the screen scratches easily, simply solved with a screen protector which I had to float on with water to avoid bubbles.

Thanks to everyone who replied. I think I now have a much better understanding.