Skip to content

Calculation used in Code-Point with Polygon (FOI241233)

This Freedom of Information request asks for details of the types of major physical features used in the calculation of postcode polygons.

Request for information - Ref No: FOI241233


We received your request on 26 March 2024.

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:

“The "Code-Point with Polygons" overview document [1] details how the postcode polygons have been automatically computed using a Thiessen process.

It says that "The boundary encloses every delivery address for which positional data of sufficient quality is available, and which follow major physical features that could reasonably be regarded as part of the postcode boundary".

Could you please enumerate the types of "major physical features" used in this calculation, and if the type has different size classes (such as roads or waterways) which classes are used and ignored.”

Our response

I confirm that Ordnance Survey does hold the information you have requested.

I confirm that the product must, “wherever it is possible without moving the boundary to the wrong side of an address, maintain the alignment of the unit postcode boundaries to motorways, railways, rivers and canals, A roads and B roads and other topological features, in that order of priority”.

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 Internal Review Officer by contacting them, within two months of receipt of our final response to your Freedom of Information (FOI) request, as follows:

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

Contact us via our FoI form

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.

The 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 you are still dissatisfied after our internal review, you can complain to the Information Commissioner’s Office (ICO). You should make complaints to the ICO within six weeks of receiving the outcome of an internal review. The easiest way to lodge a complaint is through the ICO website.