My goal is to create a map of coves and anchorages for cruising boats (sailors mostly). The bottoms need to be accurate to about a foot, so that a deep keel vessel can move about without hitting the bottom and measure anchor scope correctly. Bottom composition isn't critical but would be a nice to have.

Two questions:
1- I understand that a Lowrance Elite 5Ti will record the bottom depth as you drive over it, but if side scan is added can depths be interpolated from the data as well?

2- Based on the answer from #1, how tight a grid is needed to provide an accurate depth map of an area?

1. No - there is no extra depth information provided by the sidescan channels, so this won't help with bathymetric mapping. It can be very useful, though, for seeing what is on the bottom around you and for helping to highlight areas that should be mapped more thoroughly.

2. To cover all of the bottom, you need to run very a very tight grid. If you consider that a standard transducer with a 20 degree cone angle will cover an area of about 1/3 your depth, then you would need to run tracks that were that distance apart. Obviously in very shallow water, this could be very close indeed and is not always going to be practical. What you need to understand about interpolated depths between measured points is that they are just "guesses". Depths at a certain position are just estimated based on the known points that surround it, and could vary wildly from reality. This is why any map produced by ReefMaster is not suitable for use when navigating, which is something that we always stress.

Great, answer. Thanks Matt!