A postcode is a series of letters and digits, defined by the Royal Mail and appended to UK postal addresses for the purpose of sorting mail.
UK postcodes usually identify a group of addresses, although in the case of a large postal user it may represent a single delivery point. In residential areas, each postcode generally represents up to about eighty distinct addresses.
STATS19 includes the facility to record postcodes of people involved in crashes.
Postcodes in MAST
Postcodes are used by MAST to relate drivers and casualties to the socio-demographic profile of the community where they live. This is done using the Mosaic Public Sector classification system.
Each postcode is also related to a location in the Geography hierarchy so drivers and casualties can be categorised by their place of residence.
Not every STATS19 record contains a postcode. These 'missing' postcodes are recorded as follows:
- In the Crash Location, Driver Home and Casualty Home dimensions, they are recorded as Unknown
- In the Mosaic Group dimension, they are recorded as Z
- In the Mosaic Type dimension, they are recorded as Z99
It is possible and sometimes advisable to filter out these unknown postcodes when performing analyses which rely on these dimensions. This is particularly true when working with indexed reports.
The Department for Transport may be willing to accept updates of postcode information from past years. This may be possible even after the normal date for closing STATS19 returns. Any police forces or partnerships which may be able to improve data quality by submitting additional postcode records are encouraged to explore this possiblity.
Postcodes and local authority boundaries
Postcode boundaries are not always congruent with local authority boundaries. As a result, it is possible for a postal address to have the same postcode as one located within the boundaries of a different county. Because STATS19 does not contain the full postal addresses of people involved in crashes, where authority and postcode boundaries do not conform MAST cannot represent residency within authority areas with absolute precision.
In order to allocate each postcode to a single local authority district for analysis purposes, each postcode is defined by a single NSGR, representing its geographical centre. In almost all cases the National Statistics Postcode Directory provides this information. As a consequence, MAST analyses assume that people involved in crashes reside in the authority where the centre point of the postcode lies, which is the best possible approximation given the granularity of available data.
Populatiobn data is also obtained at postcode level but only represented in MAST at authority level. Therefore exactly the same technique to calculate the population figures which form the basis of indexed reports.
For the postcodes that are in the Post Office file but not on the NSPD we do some work to allocate them to the correct LAD
A postcode is made up of a combination of letters and numbers in one of the following ways:
* A1 2BC * D34 5EF * GH6 7IJ * KL8M 9NO
The same code is usually used for a small group of addresses so is not unique to every address but helps to pin-point exactly where the item of mail needs to go to.
How do postcodes work?
Each part of the postcode provides step-by-step information about where the item of mail is heading. From left to right the postcode narrows down its destination.
For example, take the postcode EC1V 9HQ:
- The first one or two letters is the postcode area and it identifies the main Royal Mail sorting office which will process the mail. In this case EC would go to the Mount Pleasant sorting office in London.
- The second part is usually just one or two numbers, but for some parts of London it can be a number and a letter. This postcode district tells the sorting office to which delivery office mail should go.
- The third part is the postcode sector and is usually just one number. This tells the delivery office to which local area or neighbourhood the mail should go.
- The final part of the postcode is the unit code which is always two letters. This identifies a group of up to 80 addresses and tells the delivery office which postal route (or walk) will deliver the item.
For further information about postcodes, refer to the Royal Mail website.