[Talk-GB] code-point_open accuracy

[Robert Whittaker (OSM lists)]

On Mon, 16 Jan 2023 at 11:50, Dave F via Talk-GB
<talk-gb at openstreetmap.org> wrote:
> Unsure if this was national policy but in my area certain organisations
> such as banks, medical centres & hotels were given unique post codes,
> presumably due to the high volume of correspondence they'd receive. Even
> though many of the properties have change businesses over the years
> (especially banks becoming eateries) they still retain their individual
> codes.

I assume that you're referring to "Large User Postcodes" here, which
are postcodes allocated to specific businesses at specific premises
that receive large quantities of mail. As well as banks,
solicitors/lawyers often have them. At least with current practice,
such postcodes should cease to exist if the business they were
allocated to stops using the premises. However, there is sometimes a
delay in the postcode being withdrawn, and the next occupant might
mistakenly start using it as the postcode still existed for the
premises at the time they moved in.

> If using the very undetailed code-point_open please don't assume that a
> restaurant in a large building with unusually high ceilings has the same
> code as it's neighbours. Local, on the round knowledge usurps the database.

I'm not quite sure what you're suggesting here. I think we should take
Code-Point Open to be the definitive list of active postcodes at the
time that version of Code-Point Open was compiled. (There are
sometimes issues with the locations it provides for each postcode, but
that's a consequence of the algorithm used to assign the locations,
rather than actual errors in the data.) Large User Postcodes should
only ever be assigned to a single AddressBase location, so the
centroid coordinates provided in Code-Point Open should (almost)
always be accurate. If a business is claiming a postcode that isn't
listed at all in Code-Point Open, then it's either a newly issued code
that has yet to make it to Code-Point Open, or the business is
mistaken and does not know its own postcode. Since postcodes are
assigned by Royal Mail rather than being a choice of the business, we
shouldn't give what the business says precedence over definitive
information that originates from Royal Mail.

As far as I know, Code-Point Open doesn't say which Postcodes are
"Large User Postcodes". However, the ONS Postcode Directory does, and
that is also an OSM-Compatible Open Data source that we can use.

Robert.

-- 
Robert Whittaker