[OSM-talk] is_in and similar tags

[andrzej zaborowski]

2009/7/28 John Smith <delta_foxtrot at yahoo.com>:
>
> --- On Tue, 28/7/09, andrzej zaborowski <balrogg at gmail.com> wrote:
>
>> What if boundary is not defined but the hierarchy is
>> defined, such as
>> with post codes?  Should people invent boundary
>> polygons based on just
>> what nodes/ways belong to the area?  I hope not.
>
> Why spend just as much time tagging every node, way and relation in an area with this information, how would that be useful when a rough polygon can essentially tag all those nodes?

Both for the time spent tagging and space used in database, perhaps
there might be some saving from using polygons but it depends on the
exact scenario.  Either way, don't add the tags you think are of no
use, they'll be added by people for whom they're useful.  Or easier to
make use of than the boundary polygons, particularly for those asking
where a place is inside a hierarrchy is_in gives the immediate answer.
 In the renderer one idea I had was to use the number of commas in the
is_in= value to decide on the text size of suburb/district labels in a
city (they could be tagged as districts, parishes, etc instead - but
you would quickly run out of tags), that's much more complicated with
boundary polygons only.

>
>> This is the case with administrative hierarchy of
>> regions/counties/municipalities in a lot of countries, in
>> other
>> countries there is no and possibly will never be any way to
>> obtain the
>> official boundary polygon information.
>
> We don't have official information available for most roads in most countries how does that stop unofficial information being added?

Well, that stops us because in this case the unofficial information is
taken out of thin air, i.e. wrong.  Say someone asks the map: am I in
county A or county B at this point?  The answer given may have 50%
chance of being wrong.

Cheers