I use the term breakline a lot but neverused the termwhere a hedge row meets a wood lot...Or where you referring to where the thicket meets the timber?.... Maybe I read your post wrong...?
If I'm not mistaken.....Joe uses the term to define ANY place where different types of vegetation meets another. A "breakline" can also be man-made...as in a fence. A river is a natural breakline. A place where evergreens meets hardwoods is a breakline. Etc...etc...etc...
Whenever I look at an aerial map.....it's the first thing I look for....and it's the first thing that catches your eye....whatever you call it. Two breaklines in close proximity form a funel. My best breakline is a place where there's a thicket on one side.....a pasture fence behind me on two sides.....and "people" on the other side of the hardwoods, in between. It's an outside corner OR an inside corner....however one wants to look at it. However viewed....it's one helluva a funnel.