Trig Pillars (FOI2523)

Trig Pillars

Request for information - Ref no: FOI2523

May 16, 2025

Information request

We received your request on 4 May 2025

We have handled your request under the Freedom of Information Act (FOIA) 2000.

A copy of your request is set out in the extract below:

“Recently a triangulation pillar was located that doesn’t appear to be included in existing maps, databases, etc. published by the OS.

The pillar appears to be a standard OS Hotine pillar including a flush bracket (bracket number 11619) and spider. The pillar is in good condition and is located southeast of Middleton in Hampshire. The grid reference for this pillar is SU 43326 42993.

In addition, approx. 460 m to the southwest of this pillar two further pillars have been found. The pillars are approximately 10 m apart from each other. Both have the standard Hotine shape with one having a spider but no flush bracket and the second not having a flush bracket or a spider. The grid references for these two pillars are SU 42906 42800 and SU 42913 42798 respectively.

Can the OS provide all information you hold on these three pillars. This includes but not limited to

OSGB grid references and indication of positional accuracy.
Any other grid references including the coordinate reference system information.
Levelling information and flush bracket height including datum.
Purpose of pillar (noting the area was once used for military training there could be a connection given the close history between the OS and the Royal Engineers)
Date of construction
Last maintenance visit by the OS to the pillars.
All other relevant and available information.”

Our response

I confirm that Ordnance Survey does not hold the information you have requested.

Advice and Assistance

However, under the duty to provide information and assistance in accordance with section 16 of FOIA, we can provide the following information which may assist you in this matter:

In the past, Ordnance Survey built pillars for other government projects for a variety of specific purposes. However, as they were not for Ordnance Survey’s use, they were never registered as being part of the national Control Archive of triangulation stations. These three pillars are examples of where OS built the pillars as part of a contract for a customer. Any information we may have once held on them would either have been deleted/destroyed and/or handed over to the The National Archives (TNA).

Next steps

Internal review

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Internal Review Officer
Customer Service Centre
Ordnance Survey
Adanac Drive
Southampton
SO16 0AS

Please include the reference number above. You may request an internal review where you believe Ordnance Survey has:

Failed to respond to your request within the time limits (normally 20 working days)
Failed to tell you whether or not we hold the information
Failed to provide the information you have requested
Failed to explain the reasons for refusing a request
Failed to correctly apply an exemption or exception

The Internal Review Officer will not have been involved in the original decision. They will conduct an independent internal review and will inform you of the outcome of the review normally within 20 working days, but exceptionally within 40 working days, in line with the Information Commissioner’s guidance.

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