Now we have all that is needed to draw the final pattern.

And here it is cleaned-up:

And matched with the aerial photo (photo (c) Lucy Pringle, remember that I had this photo visible in the perspective view all the time I was making the analysis):

The only part that doesn't quite match is the ring around the small circle in the other end of the lightning. This ring seems a bit irregular and it's difficult to tell how it's "supposed" to be.

Finally, let's see a possible message contained within this symbol...