The approximate number of records, and average number of Postal Address File (PAF®) delivery points (which broadly equate to Census households), for each level of the postal hierarchy are given below:
Level
Example
Number of records
Average number of delivery points
Unit Postcode
AB54 6DX
1,600,000
16
Postcode Sector
AB54 6
ca 9,000
2,888
Postcode District
AB54
ca 2,700
9,630
Postcode Area
AB
121
214,876
Naturally, there is considerable variation around the mean for any given unit postcode, postcode sector, postcode district or postcode area. This variability is a function of population density.
For example, there are many more delivery points in the North London postcode area N (taking in most of the densely populated borourgh of Islington) than there are in the sparsely populated rural North of Scotland postcode area IV (Inverness).
It is also worth noting that, as new housing is developed, the allocation of addresses within postcodes is continually revised by the Royal Mail. Consequently, any data (such as 1991 Census counts) aggregated to postcode sector, district or area levels must be re-aggregated as postal geography alters.
