iPostcode Support Page

Explanation of iPostcode logic

When using iPostcode it is possible the postcode displayed in the number 1 position is not the postcode you are actually in. This page has been put together to try to explain some of the scenarios which may cause this to happen.

There are three factors to consider when determining how accurate the postcode list is likely to be :

  1. The accuracy of the GPS unit built into the device,
  2. The accuracy of the underlying postcode data used by ourselves,
  3. Your proximity to other nearby postcodes and the shape of the postcodes you are in or near.

Whilst the iPhone is an extremely capable device the GPS unit is not 'professional grade' and may not always be accurate, particularly in built-up or heavily wooded areas.  In order to combat this we provide an immediate visual indicator if the location is not as accurate as needed to determine a good location by colouring the background of the postcode list either red (poor accuracy), orange (medium accuracy) or green (good accuracy).

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In addition to this the underlying data we use from the Royal Mail to provide the list of postcodes near to your location is only accurate to the nearest 100m.  Very small postcodes, or heavily crowded areas such as housing estates or city centres with many postcodes in a small area may make it difficult to accurately determine the nearest one to your location.

Finally the way that postcodes are 'geocoded' (i.e how the location and hence map co-ordinates of a particular postcode are determined) also has a direct bearing on which postcodes are displayed.  For example imagine the scenario below :

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This diagram represents two streets and two postcodes, with the dark green houses being postcode 'A' and the orange houses being postcode 'B'.  The centre (or centroid) of the shape encapsulating all the houses or buildings in that postcode is then used as the location that represents that particular postcode.  In this case the green dot and orange dot illustrate the actual map coordinates used to represent postcodes 'A' and 'B'.

If you, and your iPhone, are located at the red dot on the diagram then whilst you may actually be 'in' postcode 'B', according to the map coordinates used to represent the postcodes, you are actually closer to postcode 'A' and this is what iPostcode will display as your nearest postcode. 

iPostcode Settings (iPhone)

iPostcode has a number of settings which you can change to reflect the way you wish to use it.  The Settings page can be found in your iPhone's Settings page :

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Tapping iPostcode displays the settings page :

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The 'Number of Postcodes to display' option allows you to select from 1,2,5,10 or 20 postcodes to display in the list of postcodes.  The default value is 10.

The 'Update filter' is used to control how often iPostcode updates the list of nearest postcodes based on the distance you have moved.  If you push the slider to the left then iPostcode will update it's list of postcodes more frequently, whereas if you push it to the right then the list will update less frequently.  i.e you will need to travel further before the list is automatically updated.

The 'Postcode link' controls what happens when you tap on a postcode in the list.  Currently you can select from Google Maps (i.e the mapping application built into your iPhone), UpMyStreet which will display a neighbourhood profile of the area that the postcode is in or finally you can build a custom URL of your own.

iPostcode Settings (Android)

On Android press the menu button on your device to bring up the Settings page, and then press the Back button to return to iPostcode :

Android Settings 

The 'Number of Postcodes to display' option allows you to select from 1,2,5,10 or 20 postcodes to display in the list of postcodes.  The default value is 10.

The 'Auto-update' is used to control how often iPostcode updates the list of nearest postcodes based on the distance you have moved.  If you push the slider to the left then iPostcode will update it's list of postcodes more frequently, whereas if you push it to the right then the list will update less frequently.  i.e you will need to travel further before the list is automatically updated. 

We hope this page has been helpful in explaining how iPostcode works, but if you have any further questions please feel free to contact us.

The data used in this application contains Ordnance Survey data © Crown copyright and database right 2012. Code-Point Open contains Royal Mail data © Royal Mail copyright and database right 2012.  

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