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A pipe is an uncommon type of 3rd or 4th order ground station triangulation mark. It is an approx 1" diameter pipe set upright and mortared into rock, protruding sub 1".

The trigpointing UK list contains 23 instances of pipe marks at Hydrographic Survey Stations as follows:

* Gigha (3)
* Islay (12)
* Jura (5)
* Kintyre Peninsula (1)
* Lewis and Harris (1)
* Gugh, Isles of Scilly (1)

All but one are in Scotland. Before 2022 there had been only one possible finding recorded in T:UK, subsequently confirmed, Meall Ard on Islay. Since then, several more have been found on Islay, and one on the Isles of Scilly.

There are 27 instances of a pipe in the OSGB36 list [1]. 22 of these are in common with the T:UK list with 5 additional and one not included. The 5 'extras' are all roof stations, classified by T:UK as Intersected Stations and all are thought to be destroyed. Descriptions of these include 'Iron Pipe', 'Vent Pipe', 'Wtr Twr' and 'Resr Syphon'. The pipe mark at Gugh is not in the OSGB36 list.


  1. https://www.ordnancesurvey.co.uk/legacy/docs/gps/CompleteTrigArchive.zip