On Jan 29, 2008 10:56 AM, Lester Caine <[EMAIL PROTECTED]> wrote:
> Robin Paulson wrote:
> > one of the tag proposals i've been working on recently has got me
> > thinking about tagging composite items, and the best way to do it.
> >
> > in the case of a large site, say a hospital, university or coalmine,
> > is there any consensus on how to collectively tag all the buildings,
> > sports fields, car parks, etc. so that they are marked individually as
> > whatever they are, but also identified as being part of a greater
> > whole?
> >
> > for instance, say i ask for all the car parks near me, it would be
> > good for my routing software to tell me that there's one nearby, and
> > for it to implicitly know it's within the boundary of the hospital.
> >
> > is this best done with relations, or is that over-complicating things.
> > can any part of osm work out all the areas a given point lies within?
> > this is subtly different to the problem of administrative boundaries
> > we were talking about recently as we generally can get good
> > information on the boundaries of entities like hospitals, etc.
>
> is_in being populated and stored is always going to be quicker to search
> than
> trying to process a multitude of complex boundaries to find out if a node
> is
> inside or outside the enclosed area? More so on larger boundaries, but non
> the
> less a university campus or hospital with multiple buildings, car parks
> and
> other points of interest will return a simple list via correct is_in
> relations, while searching for nodes within boundaries my not actually
> give
> the right results were nodes are within the boundary area, but not
> actually
> defined as part of the whole.
>
> That is not to say that a set of is_in relations can't be generated from
> the
> graphics. Just that there may need to be a means of editing the results.
> Which
> is why I'm convinced that correctly managed is_in hierarchy is essential
> long
> term.
>
>
Well, that's not in keeping with the principle of being easy on the mappers.
Requiring everyone to tag every entity with an is_in tag seems unworkable
and brittle to future change. What do you put in that tag? Which admin level
or whatever do you pick? What if you decide to change it later? Not
insurmountable problems, to be sure, but it seems like a lot of extra work.
Providing boundary information ("what boundaries contain this node?") is not
necessarily a function that the main API has to provide. Boundaries could be
processed offline from a planet dump and then maybe set up with a web
service for querying.
Karl
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