[OSM-dev] Straw man design for OSM postcode database creator

Simon Hewison simon at zymurgy.org
Tue Feb 5 11:18:20 GMT 2008

Gervase Markham wrote:
> John McKerrell wrote:
>> I haven't been paying attention to this so I'm not trying to pass  
>> judgement here, the claim about "most towns, at least don't have more  
>> than one street of any name" piqued my interest though. 
> Yeah, that was probably an over-reaching claim. But I don't think it's 
> necessary for it to be true for the plan to work pretty well.

Having seen how Royal Mail do this, they introduce extra, optional fields 
between the street name and the town name, which are called something like 
"Locality", then to make sure it's still unique, there's "Locality Dependent", 
and "Locality Double Dependent".

It's been a while since I've had much dealings with that dataset, and I don't 
have access to it to do much analysis.

That said, for postal addressing, if you use the postcode, they don't really 
care about which station road you mean, so you don't need to state that it's 
Station Road, Finchley Church End, London N3 2SA.

They can do fine with Station Road, London N3 2SA.

In the absence of a postcode, Royal Mail will attempt to deliver the letter is 
you include some sort of locality hint, so they will probably know that the N3 
postcode area is known colloquially as a number of names "Finchley Church 
End", "Finchley Central", "Finchley".

For the curious, there are 18 distinct Station Roads in the London postal 
districts (from an example I gave someone years ago).

So, for a OSM postcode database creator that takes a list of assumed good 
postal addresses, we can probably locate a way that matches the name, but in 
many cases there will be multiple hits in a given postal town, in which case, 
it would need to work out the "outward" part of the postcode, and look in that 
region for the particular Station Road.

In many cases, we'll have multiple ways in the database for the same street - 
for instance, when the street goes over a bridge, or when the street is a dual 
carriageway.. And anyway, a way can have more than one postcode as well.

Simon Hewison

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