Re: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)

[Ed Avis]

Andy Robinson (blackadder-lists  writes:

>>OSM's coverage of streets is much better than its coverage of buildings.
>>Might it make sense to tag postcodes on ways?
>
>Nope, streets often have more than one postcode for the properties on that
>street. It's not the street that has a postcode anyway, it's the delivery
>points for the mail, i.e. the letterbox in your front door.

That is true.  But given that in many areas we have good streets but not good
buildings, there may be value in adding a simplified version of the postcode
data in which a way is tagged with the postcode(s) that apply along it.

The use case I am thinking of is the common 'enter your postcode' on business
websites or over the telephone.  Given a postcode you can find the street (or
streets) which it corresponds to.  This means that a house number plus postcode
is sufficient to make the whole address.

A simplified tagging of postcode=x;y on a way would let OSM be used to map
postcode to street name.  It would not be quite as precise as the PAF,
giving two possible streets in some cases where there is only one in reality.
But it might be useful for small organizations who want to give people an easy
way to enter their address, without paying for the PAF data.  (Potentially, a
web service could offer this lookup and feed back statistics on which streets
were chosen, to be used to fix up the OSM data.)

By no means should tagging postcode on ways replace the more thorough building-
by-building survey with street numbers, but it might be a first step, just as
we usually tend to put the street network in first with no buildings and come
back for the extra detail later.

-- 
Ed Avis 


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Re: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)

[Andy Robinson (blackadder-lists)]

Ed Avis [mailto:e...@waniasset.com] wrote:
>Sent: 15 February 2011 5:40 PM
>To: talk-gb@openstreetmap.org
>Subject: Re: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)
>
>Andy Robinson (blackadder-lists  writes:
>
>>><http://www.raggedred.net/codepoint/>
>>>
>>>I see - so you can use your judgement to work out the area of a
>>>postcode based on its centroid and the streets and buildings nearby.
>>
>>
>>It's not that simple. You need to do the ground survey first to get the
>>house numbers and work out which property "belongs" to which street.
>
>Ah, right.  I thought it sounded too good to be true!  Jerry C. also
pointed out
>that house numbers have to be present.
>
>So the ground survey is to add the house numbers - or I suppose just
>addr:street would be sufficient in most cases? - and then the armchair part
is
>putting those together with the code point data to find buildings in a
particular
>postcode.
>
>OSM's coverage of streets is much better than its coverage of buildings.
>Might it make sense to tag postcodes on ways?

Nope, streets often have more than one postcode for the properties on that
street. It's not the street that has a postcode anyway, it's the delivery
points for the mail, i.e. the letterbox in your front door. Hence why I only
tag the building with the full postcode.

Cheers
Andy


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Re: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)

[Ed Avis]

Andy Robinson (blackadder-lists  writes:

>>
>>
>>I see - so you can use your judgement to work out the area of a postcode
>>based on its centroid and the streets and buildings nearby.
>
>
>It's not that simple. You need to do the ground survey first to get the
>house numbers and work out which property "belongs" to which street.

Ah, right.  I thought it sounded too good to be true!  Jerry C. also pointed out
that house numbers have to be present.

So the ground survey is to add the house numbers - or I suppose just addr:street
would be sufficient in most cases? - and then the armchair part is putting those
together with the code point data to find buildings in a particular postcode.

OSM's coverage of streets is much better than its coverage of buildings.  Might
it make sense to tag postcodes on ways?

-- 
Ed Avis 


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Re: [Talk-GB] Armchair-mapping postcodes

[Jerry Clough : SK53 on OSM]

On 15/02/2011 17:23, Ed Avis wrote:

Andy Robinson (blackadder-lists  writes:


Great work!  How can you tell when you have every postcode and is there

some way of checking them against the OS OpenData postcode centroids?

Just by being systematic. If you have Chillly's codepoint postcode layer
sitting over BING its easy in the editor to assign the postcodes as you see
them when adding buildings.



I see - so you can use your judgement to work out the area of a postcode based
on its centroid and the streets and buildings nearby.

Since this isn't using any kind of ground survey to check the data, I wonder if
it would be a suitable task for a bot?  A program making guesses about postcode
areas might not be any more fallible than a human doing the same task.  Of 
course
it could only be done in areas that had already reached a high standard of
completeness, ideally with buildings traced as well as streets.

Or, perhaps, the robot could make suggestions which a human would then accept or
reject, so that 95% of the area could be covered, with human assistance for the
last few tricky bits.

This just doesn't work. The example I pointed to has shared 
semi-detached house which have different postcodes: there is no way in 
which any program could work this out, unless it already has 
housenumbers which have been mapped using, /inter alia/, shoe leather. 
Adding postcodes to ground surveyed data is relatively trivial, do not 
assume that the operation is commutative.
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Re: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)

[Andy Robinson (blackadder-lists)]

Ed Avis [mailto:e...@waniasset.com] wrote:
>Sent: 15 February 2011 5:24 PM
>To: talk-gb@openstreetmap.org
>Subject: [Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)
>
>Andy Robinson (blackadder-lists  writes:
>
>>>Great work!  How can you tell when you have every postcode and is
>>>there
>>some way of checking them against the OS OpenData postcode centroids?
>>
>>Just by being systematic. If you have Chillly's codepoint postcode
>>layer sitting over BING its easy in the editor to assign the postcodes
>>as you see them when adding buildings.
>
><http://www.raggedred.net/codepoint/>
>
>I see - so you can use your judgement to work out the area of a postcode
>based on its centroid and the streets and buildings nearby.
>

It's not that simple. You need to do the ground survey first to get the
house numbers and work out which property "belongs" to which street. Once
you know that you can then assign the postcode. All the area of B72 I mapped
out has been walked to get the building numbers first.

Cheers
Andy



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[Talk-GB] Armchair-mapping postcodes (was: B72 is a wrap)

[Ed Avis]

Andy Robinson (blackadder-lists  writes:

>>Great work!  How can you tell when you have every postcode and is there
>some way of checking them against the OS OpenData postcode centroids?
>
>Just by being systematic. If you have Chillly's codepoint postcode layer
>sitting over BING its easy in the editor to assign the postcodes as you see
>them when adding buildings.



I see - so you can use your judgement to work out the area of a postcode based
on its centroid and the streets and buildings nearby.

Since this isn't using any kind of ground survey to check the data, I wonder if
it would be a suitable task for a bot?  A program making guesses about postcode
areas might not be any more fallible than a human doing the same task.  Of 
course
it could only be done in areas that had already reached a high standard of
completeness, ideally with buildings traced as well as streets.

Or, perhaps, the robot could make suggestions which a human would then accept or
reject, so that 95% of the area could be covered, with human assistance for the
last few tricky bits.

-- 
Ed Avis 


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