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Triangulation stations

FOI14586 – Request for information


Thank you for your email of 11 September 2015, requesting the following information in accordance with the Freedom of Information Act (FOIA) 2000:

1. The position, elevation, type, access requirements, current state and any other information held about triangulation stations, both current and disused, in machine readable form (CSV or equivalent).

2. To the extent that it is held, construction details of each type, specifically relating to any mounting points provided for survey equipment (dimensioned engineering drawings would be ideal).

Our response

I regret to inform you that Ordnance Survey is unable to help you with your enquiry as we do not hold this information.

However under our duty to provide advice and assistance as stipulated in Section 16 of the FOIA, we can provide the following explanation which may assist you in this matter.

The Trig Archive is considered a legacy database and is not one which is maintained. Ordnance Survey only holds a digital copy of the Trig Archive which I have attached. This includes limited details on each Trig station, however does include all Trig marks and not just pillars.

Full details are held in the (physical) office files for each Trig mark. Nearly all 32,000 (approximately) files are archived at The National Archives, the only exception being the Primary Pillars which are held in offsite storage on route to The National Archives.

I have also attached some diagrams (Zip file) showing the design of the three main types of Trig pillar - normal, circular and natural stone types.

We do not hold the technical drawings of the design of the 'spider', the brass 'forced centring' device set in the top of a trig pillar, however may be held at the National Archives.

Please contact:

The National Archives,
TW9 4DU.Tel: +44 (0) 20 8876 3444


Tel: 020 8876 3444

I hope the above is of use to you.

Internal review

Your enquiry has been processed according to the Freedom of Information Act (FOIA) 2000. If you are unhappy with our response, you may request an internal review with our FOI Internal Review Officer, by contacting them as follows:

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

Email: foi@os.uk

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 FOI 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.

The FOI Internal Review Officer will either: uphold the original decision, provide an additional explanation of the exemption/s applied or release further information, if it is considered appropriate to do so.

Appeal to Information Commissioner's Office (ICO)
If, following the outcome of the internal review you remain unhappy with our response, you may raise an appeal with the Information Commissioner’s Office at:

The Case Reception Unit
Customer Service Team
The Information Commissioner’s Office
Wycliffe House
Water Lane

Email: mail@ico.gsi.gov.uk

Telephone helpline: 0303 123 1113 or 01625 545745 for advice, Monday to Friday.

Thank you for your enquiry.

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