[OSM-talk] administrative boundaries and is_in
siliconfiend at gmail.com
Wed Jan 9 22:58:25 GMT 2008
On Jan 9, 2008 12:44 PM, Robin Paulson <robin.paulson at gmail.com> wrote:
> can someone explain a few things about the way boundaries work, and
> their relation to the is_in key?
> as far as i can tell, when a location (say the suburb of balham, in
> london) is added to the map, the is_in tag needs to be set, multiple
> times. in this case, it would be set as follows:
> is_in:Westminster (...i think)
> is_in:greater london
> which seems counter-intuitive, not to mention requiring huge amounts
> of work. do we set this for every item - roads, churches,
> supermarkets,....thousands of other items?
> is there anything underway to enable OSM to calculate where an object
> is, based upon knowledge of administrative boundaries - after all,
> they are only a polygon-shaped bounding box?
> if i set is_in of balham to london, and the is_in of london to
> england, does osm know that balham is therefore in england, by
> cascading the is_in values? and so on, for as many levels as we
I think the is_in tag is mostly useless, for the reasons you've
demonstrated. I've been thinking about this problem, too. In order to make
properly indexed streets (for find by address) and POIs for GPS devices (I'm
thinking Garmin here specifically), each point or street needs to be
associated with a region (i.e., state or province or maybe country), city,
zip code, etc. But this doesn't need to be tagged on each point--it should
be able to be derived from boundaries. I'm thinking of a program which uses
the administrative boundaries already in the planet file to do an optimized
lookup for points. You could query it for admin_level=4 to get the state or
province name, to take an example from the "boundary" key page on the Wiki.
(Does anyone know why there are only even numbers for the admin_level
This is basically reverse geocoding, and I know some work has been done on
it in other projects in the past. Maybe PostGIS would be good for this (I
don't know much about PostGIS, but it seems to be the sort of thing for
which it was created).
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