I occasionally get asked questions about the UK postcode data I provide on the site, so I thought I'd give the answers to some of the common ones here.
Where does the data come from?
Most of the data comes from Ordnance Survey as part of their OS OpenData initiative.
You can download the
Code-Point data set directly from them.
The Northern Irish data (BT district) comes from the
Northern Ireland Statistics and Research Agency.
Why are the GY, IM and JE districts missing?
The Ordnance Survey data doesn't include the GY, IM and JE districts,
even though they are part of the postcode system. As yet I've been unable to source the data for these postcode areas.
Postcode XX1 2ZZ isn't in the data, why not?
The Ordnance Survey data doesn't include postcodes that are no longer in use so it
might be you've got an old postcode that has been removed from the data.
Check the postcode on the Royal Mail website to see if it's still in use.
Alternatively, your postcode may be newer than the OS data, which isn't updated very regularly.
Postcode XX1 2ZZ isn't in the data but if I use the geocoding tool, I get a location returned, why?
The geocoding tools don't use the same database to do their work, they use the Google Maps geocoding API.
From my experience, this API will return an approximate location for a postcode,
even if the postcode doesn't exist. For example if XX1 2ZZ doesn't exist, the Google Maps geocoding API will
return the general location of the XX1 postcode area.
Some postcodes have the same latitude and longitude, why is that?
Generally this will be because the postcodes are non-geographical postcodes,
used for PO boxes etc. The latitude and longitude provided will be the location
of the associated post office.
The address shown on the map for a postcode doesn't match up with the postcode, why?
The approximate address comes from the Google Map reverse geocoding service so the
postcode may not match up with the original postcode you were looking at.
This will often occur when you're looking at a non-geographical postcode which shares
its location with several other postcodes.
What datum is used for the latitude and longitude?
The latitudes and longitudes use the WGS84 datum.
Why does the Northern Irish data use GB grid references instead of Irish grid references?
Northern Ireland isn't part of the GB grid reference system so the values shown are
artificial (although Northern Ireland could fit within the GB grid system) but I figured
that was a preferable solution than the data using inconsistent systems.
If I download the CSV file containing all postcodes, only the first 65536 rows are displayed when I open
it in Excel, where's the rest of the data?
Older versions of Excel can only deal with 65536 rows of data in a file. The rest of the postcodes are in the file but you will need to
view them using an application that can show all the rows or download the CSV files for specific areas that contain fewer rows.