[Talk-GB] A quirk of UPRNs

[SK53]

The other day whilst processing the UPRN table to find locations with more
than 1 UPRN I happened to notice an odd thing: some UPRNs have integral
eastings & northings, whereas others have these fields to 2 decimal places.
OS Master Map has a horizontal RMS error of around 25 cm, so the precision
of these suggested that they had not been derived directly from Master Map.
My suspicion is that these are converted WGS84 values.

Anyway, I took a closer look. I filtered all those with non-integral
eastings (round(eastings) | = eastings is what I used) for all Wirral
UPRNs. I already have a flag as to whether these UPRNs are within a
building from Open Map Local. The results were interesting: 144k uprns with
integral eastings, 39k without. The ratio of in building UPRNs in each
group was roughly 1:20 compared with 1:4.

I've been exploring this data within CH45 (New Brighton & Wallasey Village)
and my tentative conclusion is that the latter class represent new URPNs
after some unknown cut-off date. The following classes of objects are
included:

* Completely new buildings (e.g., in-fill housing on former tennis courts)
* Buildings split into flats
* Some retail premises with flats above (change in scope, possibly)
* Classes of street furniture (which presumably moved to being 'in scope'
for UPRNs): phone boxes, sub stations, pillar, and at least one lamp, post
boxes, CCTV cameras, bus shelters.
* At least one, where a building has disappeared from OS Local

For a postcode district the number of such UPRNs is reasonable to explore
by hand: I created a geojson file which can be viewed in any editor (and
stepped through in PL3 & JOSM). As usual I'm using this area because I know
it, have done some mapping & it is covered by Bing Streetview. Presence of
the latter is important for checking one's initial assessment of what a
UPRN-referenced object might be.

I also noted a telephone kiosk which I'm pretty sure was not present in
2016 has an active UPRN (as checked against findmyaddress), and some
buildings on Bing (with UPRNs) dont seem to be present in OS Map Local.

You may find this little bit of info of some use in your own area (e.g.,
helping spot missing new builds). I need to find out roughly when the
change in format occurred, but I don't know the Wirral well enough to do
that.

Jerry
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