Trig on current 1:25,000 mapping that has never existed

[lejogger]

Hi all, maybe someone can answer this one. On the current HD 1:25,000 OS map a trig pillar symbol is located at grid ref SY47089131. As far as I can tell, this has never been a location for a trig, and makes little sense because there is another nearby extant prominent trig pillar with good sight lines to all surrounding trigs on North Hill at grid ref SY47989067. There's no record of it on older maps or in any databases so I'm wondering if this might be a cartographer's mechanism to ensure maps aren't being copied, or maybe just a mistake. Or some other reason? Any ideas?

[agentmancuso]

There is in fact a triangulation station at this location. OS Maps used to show non-pillar trigs too, as black triangles identical the ongoing triangulation pillar symbol in every respect bar colour. When these were removed in bulk a few slipped through the net, and ended up as blue triangles, sometimes referred to as 'phantom trigs'; this looks like one of these.

[lejogger]

Thanks for the update on that - my interest has only ever been the pillars, so haven't kept abreast of other stations, their history and symbols.
It would be interesting to know if anyone has done any digging into how many 'phantom trigs' there are currently on the maps....

[agentmancuso]

I doubt there's any firm answer to that, but my impression would be a matter of dozens. I can think of a few off the top of my head, and there are almost certainly others like yours that nobody has every noticed before (afaik).

[Itchy-trigger-finder]

There is a trig symbol on the map at Flamborough Head that isnt a pillar (from memory it is the weather station on the lighthouse roof) and I think Stannage Pole is also shown on the map as a pillar when it is actually (as the name suggests) a pole.

[paulxtr]

A triangulation pillar symbol is shown at Saskills (SD 39521 84315) on the current OS 1:25k map. I noticed it whilst planning a recent cycle tour of the Lakes. There's a bolt (TP7523) at that location but a pillar has never existed there.

Cheers,
Paul