[OSM-talk] is_in and similar tags
David Earl
david at frankieandshadow.com
Tue Jul 28 16:09:06 BST 2009
John Smith wrote:
>
>
> --- On Tue, 28/7/09, Shaun McDonald <shaun at shaunmcdonald.me.uk>
> wrote:
>
>> Only use the is_in tag on the place nodes rather than every node.
>
> Why?
>
> The reasoning I've been given so far is for routing, but to find such
> information routing software would have to look at all nodes near by
> until it found the node tagged with the place information.
The reason I gave was for name searching, not routing. It allows the
result of a search to be given a descriptive context that isn't
currently possible any other way. This already works and it is a shame
to break it because of dogma.
Given a place (or any other object, but as Shaun said, places are the
key things), determining for every place which county, state, country a
place is in is complicated and will take a lot of compute resources. It
amounts in principle to comparing each point against every boundary
polygon in the world. Yes there are optimizations and short cuts, but it
will nevertheless be a lot of work to do. And given that places don't
move around significantly, we'll want to store the result in order to
avoid recomputing it every time - and we have a natural place in which
to store it already.
We can give ourselves a helping hand here if we keep is_in.
David
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