On 2014-06-24 05:52, Brian Quinion wrote:
Hi,
So from my point of view as a nominatim developer the issue is that
there are (at least?) 2 types of city in the USA.
There are administrative cities and there are postal cities. There
are also census areas, which may or may not be their own category of
thing.
At the moment all of these are tagged in exactly the same way:
boundary=administrative
type=boundary
plus an admin_level
There is nothing that lets us tell them apart so we are left to pick
the 'best' city.
"Postal cities" aren't currently tagged as areas, only tag values on
individual POIs and buildings. Clifford's first example is a building
that lies outside the Redmond city limits but still carries a Redmond
address, which is noted in addr:city.
Would it be possible for Nominatim itself to synthesize a "postal city"
boundary for its own use? I'm unfamiliar with Nominatim's inner
workings, but it appears to models streets as polygons. How about
something similar at the city level, taking into account the city limits
and any matching addr:city values within a certain radius?
There's at least some support on this list for making all CDPs
boundary=census or somesuch instead of boundary=administrative. It's
been used extensively in some areas. [1] The Standard stylesheet no
longer renders automatic "catch-all" labels on large areas, but perhaps
the openstreetmap-carto developers would entertain a style rule for
boundary=census and/or place=locality areas.
Adding individual 'city' tags to houses doesn't help much. Do you
mean admin city or postal city? Same issue. In most cases we actually
want to find and link to both.
addr:city tags always indicate the postal city. boundary=administrative
areas always indicate the city's administrative limits. Anything else
should really use is_in:city.
So - my suggestion would be to introduce tagging that makes the
distinction. Ideally to create boundary=postal or something like that
rather than tagging every road or house with duplicate information.
A "postal city" in the U.S. is just one of possibly several names
associated with a ZIP code, which is an area by first approximation but
technically a route. [2] boundary=postal sounds a lot like the USPS's
ZCTAs; otherwise, who knows the exact boundaries of their own ZIP code?
I mean, are there "Welcome to Boston Mass 02134" signs anywhere?
Administrative boundaries are contentious enough on this list, but
realistically, ZCTAs could only ever be added and edited by bots. Sounds
like the perfect candidate for an external database. ;-)
In adding a tag like addr:city, I'm making a statement about an
individual POI's address carrying a certain city. That's often more
verifiable (via signage, business cards, or takeout menus) than a
statement that every address in a large polygon carries that address.
How precise is that polygon?
The standard way to avoid maintaining redundant data is through a
relation, like associatedStreet relations, but I'm not keen on adding
every building or street in town to a relation.
[1] http://taginfo.openstreetmap.org/tags/boundary=census#map
[2]
https://lists.openstreetmap.org/pipermail/talk-us/2009-December/002567.html
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