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Former chalk quarry

FOI14611 – Request for information


Thank you for your email of 1 December 2015, requesting information from Ordnance Survey in accordance with the Freedom of Information Act FOIA 2000:

I am told there was (aerial) survey in 1992 which would have located for mapping the quarry edge of a former chalk quarry a Nether Hale, Birchington.

If this is correct:

1. Could you provide the date of survey?

2. The ground positioning accuracy of the quarry edge feature?

Our response

I can confirm that Ordnance Survey does hold the information you have requested. I am pleased to provide you with the below information with regards to your request.

1. The last new edition of 1:2500 - TR2867 which covers the former chalk pit was 1961.

There was a Survey Information on Microfilm (SIM) edition dated 11/10/1993 produced for TR2867 but we are unable to tell if any change was made to the chalk pit at this time.

Looking back through old flight diagrams it appears that flying was undertaken in this area of Kent in 1994 and 1995, however, that doesn’t necessarily mean that any of those sorties were used to update the mapping for the chalk pit.

2. The chalk pit would have been captured to 1:2500 mapping tolerances. Under our duty to provide advice and assistance as stipulated in Section 16 of the FOIA, we can provide the following which shows our accuracy statements from the OS website. The 1:2500 scale has been highlighted for you.

We define accuracy in three ways:

Absolute accuracy – how closely the coordinates of a point in the dataset agree with the coordinates of the same point on the ground (in the British National Grid reference system).

Relative accuracy – positional consistency of a data point or feature in relation to other local data points or features within the same or another reference dataset.

Geometric fidelity – the ‘trueness’ of features to the shapes and alignments of the objects they represent - when testing the data according to the dataset specification against the ‘real world’ or reference dataset.

The following table represents the absolute and relative accuracy applicable to the scale at which the product was surveyed.

Original survey scale

99% confidence level

95% confidence level



Absolute Accuracy

0.9 m

0.8 m

0.5 m

Relative Accuracy

+/- 1.1 m (up to 60 m)

+/- 0.9 m (up to 60 m)

+/- 0.5 m (up to 60 m)


Absolute Accuracy

2.4 m

1.9 m

1.1 m

Relative Accuracy

+/- 2.5 m (up to 100 m)

+/- 1.9 m (up to 100 m)

+/- 1.0 (up to 100 m)

1:10 000

Absolute Accuracy

8.8 m

7.1 m

4.1 m

Relative Accuracy

+/- 10.1 m (up to 500 m)

+/- 7.7 m (up to 500 m)

+/- 4.0 m (up to 500 m)

*RMSE (root mean squared error) is the square root of the mean of the squares of the errors between the observations.

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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