If we see them as observation points rather than churches it would make more sense perhaps.
If an islet a mile or so out from the coast is used for observing the coast it would have quite a wide span of coastline covered as well as whatever was to be seen on the distant skyline.
Depending on the distance they should be able to keep an eye on any other structures built off the coast on either side. A bit like the old signal points which were positioned to send messages by fire along the coast.
They would be multi purpose no doubt. Perhaps a small community of specialists. Some for observations of one sort or another, some for Customs duties, others for defence/maintenance etc.
There are supposed to be forty three around the coast. Would that be enough or are some missing?
If they were involved in ancient map making they would use the same old triangulation techniques used today. I'm sure I read somewhere that the druids knew about Pythagoras and also used Greek letters for certain things.
Over at Orkney Dr Euan MacKie claims that recent finds have vindicated his belief that there was a settlement of astronomer priests.
http://www.orkneyjar.com/archaeology/20 ... riesthood/
The remarkable archaeological discoveries on the Ness of Brodgar are proof that an elite group of astronomer priests once held sway over Orkney.
That’s according to Dr Euan MacKie, an archaeologist and prehistorian, who visited the ongoing excavations on the Ness last summer.
In 1977, Dr MacKie suggested in a book that Skara Brae might be the home of a privileged, theocratic class of wise men and women who officiated at astronomical and tribal ceremonies in and around the Stenness rings and who were supported by the agricultural population.
Given the standard of the buildings in the area at such an early period it should not surprise us if tidal islands were indeed man made.
At Orkney they are now investigating drowned structures discovered by modern sonar and scanning techniques.http://www.orkneyjar.com/archaeology/20 ... ness-loch/