Here's what I think the OP is getting at:

http://home.maine.rr.com/rlma/Vector.jpg

CAD, which I also use a lot is vector based so lines are mathematically
thin. They don't get thicker as you zoom in. The view on the left, drawn
with CAD, is true scale so the boat is a comfortable distance from the
sounding line.

In the view on the right, the line is zoomed 1000 times. If the system
generated icon showing your boat doesn't scale at the same time as the view,
you get an image which makes it look like you are still a comfortable
distance off. But, it this view, the distance to the sounding line is only
a few inches. Throw in normal chart inaccuracy and, THUNK!

--
Roger Long