Fishfinders for Dummies?

[Cowpokey]

I don't have any experience with maps of Tri and Rocky... my lower end Lowrance won't provide charts for fresh water lakes, I think the higher end models have "chips" than can upgraded and purchased for inland lakes that are detailed.

Its pretty much like the maps you see here....
http://www.navionics.com/en/webapp
when you zoom in you see a lot of detail. The more expensive the FF/GPS the more detailed the maps.
But I have been very happy with my low end $149 Lowrance black and white detail.

I just checked that link... you can view Tridelphia and Rocky Gorge quite well.
So I am pretty sure you can get detailed maps to plugin to your FF/GPS.
You'll just have to spend more money than $149....

The base map on my unit has the same detail as what the link shows.

[J.A. Veil]

The Lowrance HDS series of units comes with extra mapping features installed. You can specify Nautic Insight (most marine waters, including the Chesapeake) or Lake Insight (most North American lakes). These units are not inexpensive, but are full featured and have lots of capabilities. The HDS-5 units occasionally go on sale for less than $500. I have an HDS-5 on my center console. The Lowrance LMS-527 unit I transferred from the center console to my kayak two years ago has an older Navionics SD card that gives good depth contour info for the Chesapeake.