NavList:

The last few comments on radar raise an interesting question. Local marine navigators like myself use 12 to 24 mile radars on smaller vessels.  

For most of us they are very range limited by mounting height.  

Primary use is collision avoidance and general positioning based on stationary targets. I spend more time on 3 miles or less vs 12 in low visibility.

My original learning was collision avoidance on a maneuvering board. On small informal boats it's now often done with visual tracking on the screen with various toys supplied for the application.

A popular addition I dislike but many swear by is radar overlay onto the GPS chart screen.

While I have some working knowledge of beam width, target shift, etc on small working radars for our plotting purposes, I have never really considered the chart vs radar beam issues on overlay radars.

Makes me wonder how this is actually plotted.

I personally like separate displays as overlay I find a distraction in enclosed waters from moving vessel traffic. I want a clear view of the screen for collision avoidance without all the chart additions cluttering my view.

My approach is to mentally cross check radar, gps, and sounder screens constantly  to verify that everything cross checks, with the good old paper chart I've used since a kid as my governing master.

My new boat still has only one large display, so overlay is sometimes advantageous. 

Is my limited radar range so small that the radar  chart plotting problem is ignored, or do these mysterious programs undertake corrections of which I am unaware. You do see visual shifts between contour charts and land radar targets.