Edges of, in this case, the land. Or possibly the edge of the ocean. It all depends on whether you are afloat or on land, and what you would prefer to avoid; grounding or wet feet.
This was based on NOAA chart 13302,and is clearly NOT to be used for navigation.
I was thinking about edges of things this week – where one object or way of thinking touches another. They can be easy to see from far away, but get less and less distinct the closer you get. Case in point: coastlines. The coast of Maine, depending on how you measure it, is relatively short, or infinitely long. The edge changes with the tides. (I won’t even mention that the tides change with the moon.) The land goes from distinctly not-ocean to distinctly submerged but passes through this interim, inter-tidal space where it could be either. Or possibly both.