[OSM-talk] Nominatim - Does it use the is_in tag?
lonvia at denofr.de
Tue Aug 16 19:27:28 UTC 2016
On Tue, Aug 16, 2016 at 02:29:26PM +0100, Dave F wrote:
> I've heard a claim from a user who still wants to use the is_in:*
> tag as well as boundary tags that Nominatim uses is_in as preference
> because "geospacial mathematics is resource intensive".
> Is this true?
Not at all. Nominatim happily processes boundaries and always prefers
it over any other hierarchy information.
It is true that it still understands is_in:* tags but prbably not in
the way you would think. First of all, they are completely ignored
on anything at building level (e.g address points and POIs). For
everything else Nominatim always uses a geospatial match when
computing the address. is_in:* is just good to help make a decision
when there are two equally well suited candidates, generally when, say,
a road is right between two city place nodes. As soon as there are
boundaries, multiple candidates don't happen anymore, so that is_in:*
is ignored for all practical purposes.
> I thought geospacial calculations were fairly light on processing power.
> I also thought is_in:* was to be discouraged. Being hard coding, if
> a boundary was to change all affected entities would become
Yes, if possible always draw boundaries. They are more precise and easier
to maintain. is_in is unnecessary.
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