In the last few days we’ve been exploring the size of the OLAF problem, starting from small, more manageable geographic entities and wondering first how many addresses we would find in one town and then how many postcodes.

What’s the size of the entire problem, though? If we could deliver a comprehensive open addresses dataset one day, how many addresses and postcodes we would find in it? The answer is actually easy.

If we assume that the number of addresses is approximated well by the number of properties in the UK, we can build our estimate by using the Office for National Statistics’ “National Statistics Addresses Lookup” open dataset (NSAL), that is an openly licensed subset of Ordnance Survey’s AddressBase commercial dataset, listing all Unique Property Reference Numbers (UPRNs). The UPRN system has the ambition to assign a unique code to anything that one might want to uniquely identify on Great Britain’s territory. “Pretty much every property in the country has a UPRN, from mansions to beach huts and ponds to life belt buoys”.

NSAL lists 36,681,879 UPRNs for Great Britain. We can reasonably assume that the number of UPRNs / properties is proportional to the number of households that is documented by the latest Census. On 27/03/2011 the number of households in the UK was 26,442,096, 703,275 of which was in Northern Ireland. Our estimate for the number of addresses in the UK is then 36,681,879 / (26,442,096 – 703,275) x 26,442,096 = 37,684,158. This finding is consistent with the Royal Mail and Ordnance Survey figures.

The number of postcodes is even easier: we just need to count the total of non-retired postcodes in the Office for National Statistics’ Postcode Directory: 1,745,801.