Hard spots

Have heard about “hard spots” for years. Way back in the late 60’s when I used flashers folks would talk about ‘ hard spots’. Could some one explain this to me? I watched a fishing show on tv the guy was running a lake at idle said there was a “hard spot” . He marked with a way point later returned to this and caught several fish. I have used flashers, paper graph, DI, and side image, plus now have live scope. not new to electronics but this one term “ hard spot” baffles me.
Wild bill

It will look "shiny" on SI

A hard spot can be an actual difference in ground composition because of a house foundation, road, rock substrate, etc. Doug is spot on, it looks "shiny" (I use the word "brighter") on SI or DI. You'll see it on 2D if you go right over it as a deeper return than the surrounding area. On our lakes, a lot of these hard spots are where current has removed the silt from a hard clay or some type of concretion.

If you are running 2D and watch the bottom contour the thicker the bottom appears the harder the surface is that you are seeing. A soft, muddy bottom will send back a return that is very thin. A hard bottom sends back most of the signal ergo the thick bottom and a soft bottom will absorb the signal sending back weaker image.

I have no trouble finding hard spots, I'm in one most always!

If you have Humminbird and run the lime green color palette, hard spots show up red.You can't make much of anything else out but it makes finding hard spots easy.

Amen brother, that’s what I’m saying!