[OSM-talk] Post code areas

[Lester Caine]

Anthony wrote:
> Hi Frederik,
>
> What are the sources for the post code areas?  How often are they
> updated?  How are they defined (by reference to houses, by reference to
> geographical features, by lat/lon, something else)?  Will this data be
> integrated into other OSM data, or is it basically just a separate layer?

Looking at the post code data that has just been 'open sourced' by the UK 
government I am beginning to realise part of the problem here. We are trying to 
create a generic solution when in reality there are distinct differences country 
to country.

"How are they defined" ... In the UK by a list of house numbers and names which 
the Post Office still maintains copyright on, so the OSOpenData 'postcode' 
information only has a lat/lon reference (codepoint), and NO address data. One 
can draw areas around the group of houses that form a postcode, but that is not 
the right way of handling them. The OSOpenData list needs to be augmented with a 
lower layer of 'house' objects. ANY boundary drawn around that group will be 
arbitrary

 From what I am seeing Canada works a similar way? But many other countries DO 
define an area for 'postcodes' which in reality are simply fairly large post 
areas defined as such, and do not (as yet) go down to define postcodes for 
smaller groups of buildings.

The US ZIP code system has a nice hierarchy of AREA information? But even it's 
ZIP4 code is not 'defined' by reference to a simple list of house ID's

Bottom line ... create 'areas' for information that is actually defined as an 
area, but keep finer detail in the format it is defined in?

Returning to Frederik's original question ... 
http://en.wikipedia.org/wiki/List_of_postal_codes_in_Germany on the whole covers 
it quite nicely. German post codes are defined by area - which do not match 
state boundaries.
BUT a common aspect to all of this is the hierarchy of course detail, with - in 
the case of Germany - 10 areas each divided into 10 sub areas. Just like the UK 
has a number of large areas defined by letters or letter pairs, each of which is 
sub divide, BUT the 'areas' so defined only loosely enclose a number of 
individually identified properties.

So we have a hierarchy of boundaries - which may or may not correspond to 
administrative boundaries - but which ARE as difficult to draw. Perhaps they do 
need their own 'layer' of data, the top rung of which is 'country' which then 
drills down through a set of larger and smaller post_boundary data. An 
'international' post code would then be prefixed with the country code so that 
one knows exactly where in the world one is when adding a 'postcode' to a location?

I have always maintained that we need hierarchic lists overlying the physical 
data so that one can search for locations in that tree, and postcode is just 
another fairly consistently defined tree?

-- 
Lester Caine - G8HFL
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