please empty your brain below

I take my hat off to dg for his research online and on the ground. The lovingly-curated map is a wonder to behold - but I struggle with the sequencing of the adjacent list of included part-postcodes, which is neither by size, by alphabet nor by geography (eg clockwise).
It's chronological, i.e. the order I did them.
Thank you dg.
You've done it.
Ignore naysayers.
Well done!
A remarkably thorough and interesting investigation. I wonder if the Royal Mail (or many couriers) know of all these locations - perhaps there's a market here?
An aside - did you have your phone on counting the number of steps needed to complete this?
Very Well Done
Well done, dg. What's your next tick-list going to be?

I do wonder why some postcode districts include areas that don't have a delivery point. It looks like the part of IG10 that's in London, for example, is a corner of Epping Forest between the Ching and the A1069. What's the point of that being in any postcode district?
You've included TW19 in your list of possibles, but you visited there in your quest.

dg writes: deleted, thanks.
The NSUL (National Statistics UPRN Lookup) file from the ONS includes a file for Greater London (NSUL_SEP_2022_LN.csv) with around 5 million "address points" (letterboxes) and corresponding postcodes and locations (10-figure grid references, so accurate to 1m). I had a look. In general, the only supposed address points for the 9 possible postcode districts are car parks, bridges, motorway layby telephone boxes, road junction signs, footpath signposts, electrical substations and water retention basins etc.

The only possible place someone might post a letter to is Browns Breakfast Bar, on the A316, it doesn't appear on the NSUL list or have a letterbox but does have a TW16 postcode - - maybe post is slipped under the door. The nearby Hampton & Kempton Waterworks Railway itself also appears to be in TW16, based on NSUL, but is accessed from a road in TW13 and its website lists the latter, too.
In my opinion, a postcode district IS the set of addresses using that postcode. To ask which district a particular oak tree is in is a meaningless question with no answer.

Admittedly maps have been drawn purporting to show postcode districts as areas of land, and these are handy and quite interesting. But they are works of imagination, and about as factual as maps of Narnia.

dg writes: I refer you to my previous response.
The quirks of using a system of gelocations set up for postal delivery to geolocate land within an administrative district (or other uses) is why what3words exists as a business (and is often used by e.g. film companies on location shoots for exactly such purposes)
Along with Malcolm, I understand that postcodes only apply to delivery addresses, not to the road or pavement nearby. So, unfortunately you probably have missed visiting many of them.

I formerly scheduled delivery of building materials and often had to explain to postcode database salesmen that building sites, roads, motorways, fields etc do not have postcodes.
What's CR9 and E77 all about?

dg writes: this.
Pedantic point: KT18 is Malden Rushett, not Maldon. You probably noticed as you walked along Rushett Lane that there is a grass airstrip on the south side of the road which is accessed from Chessington Road. I've driven along Rushett Lane many times but only once seen a plane take off.

dg writes: fixed, thanks.
The airstrip was not distinguishable from the road.

Of course, now you need to visit that little bit of E4 that is outside Greater London.
Starting from the point of view of Malcolm of Kent and Kev, that a postcode district is a set of mail delivery points, then it possible to define an area - with boundary - that encompasses them (and excludes others); and at district level it is often appropriate, for utilitarian purposes, to do so. But the question is what about the space between delivery points in different districts: is it not in either district, or is the boundary between them drawn arbitrarily (based on some algorithm or not)?

In the later case, then there will be parts of a postcode district, around the edge, that do not contain a delivery point. And if that part is defined by postcode district boundary and the GLA boundary, then it is 'in scope' for this project, and should be visited, i.e. the exclusion of areas without delivery points is incorrect.

What the Royal Mail's 'official' position on this is I've no idea, but absent an 'official' boundary definition from them, then any map showing boundaries (without an intermediate space) is purely unofficial and arbitrary - for utility and not definition.
...and avoiding philosophical arguments like this is why I had rules, specifically "To be included, a postcode district needed to have at least one postal address within Greater London."

Not every borough is as helpful as Kensington & Chelsea who've produced, really quite definitively I think, a map clearly showing all the postcode districts across the entire borough.
The bit of E4 outside Greater London was that bit of High Beech/Sewardstone that was best reached by the postman walking from the Chingford sorting office (which was/is opposite the Station). The bits reachable best from Loughton sorting office, then in Forest Rd, eventually found themselves in IG10. The rest went into Waltham Abbey (and hence EN9), and I hope they issued the postie there with a bike.
There is a poignant account of the widow of the poet, Edward Thomas, receiving the fateful telegram by the District Messenger from Loughton, and having to trek back to send telegrams to all his friends, as only from Loughton PO, then next to the sorting office, could you send telegrams, not from High Beech itself.
Thanks Ollie, it's great to have some proper data!

If Brown's Breakfast Bar was at the other end of its layby it'd be in Surrey, but the north end is (just) in London and it has a Food Hygiene Certificate issued by Hounslow council, so that does look pretty convincingly TW16.

It'd be interesting to know which of the other eight questionable districts have car parks, bridges, motorway layby telephone boxes, road junction signs, footpath signposts, electrical substations or water retention basins within Greater London and which don't, just to get an absolutely definitive list. But it's good to know I (officially) don't have to visit any of them.
NSUL sometimes throws up oddities. For instance it says the cricket pitch on Putney Lower Common is the only SW13 postcode in Wandsworth but the website for Putney cricket club says the postcode is SW15.
CR9 1HT does seem to be the postcode for Croydon Post Office...
There are at least two dozen buildings with a CR9 address scattered around Croydon, but non-geographically which is why I chose to exclude them.

If anyone else wants to attempt this challenge and throw in EC50, CR9, CR44, CR90, E77, E98, N81, NW26 and UB18 then feel free.
Superb! Time to collect your GIR 0AA.

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