[Talk-us] understanding administrative boundary relations

[Toby Murray]

The area you linked to has no boundary data in OSM. You don't state
this in your email but by pulling up the TIGER shapefile, it looks
like you are wanting school district boundaries? I see one runs
through the area you linked to, in the shapefile. School districts
were not imported into OSM. The only things that were imported from
TIGER is roads, state, county and city boundaries.

Administrative boundaries in OSM have always been a tricky subject.
OSM thrives on information that can be verified by someone standing on
the ground, looking around and seeing something that can be put into
the map. Administrative boundaries are (usually) not that way. They
are imaginary lines drawn on the map. Sometimes they follow physical
features but often they don't. So the only source to verify or update
them is to go back to the imaginary line drawer and ask for an update.

Because of this, I think boundaries in OSM tend to deteriorate in
quality quicker than other features. Sometimes people modify a way
that is part of a boundary relation and don't realize that they are
affecting the boundary. I have done a lot of work fixing up boundaries
(mostly county) across the country and there are definitely a million
ways to break them.

If you want an example of an admin boundary in OSM, here is the
Sunnyvale city boundary relation:
https://www.openstreetmap.org/relation/112145

Toby


On Thu, Sep 3, 2015 at 5:40 PM, Ray Kiddy <ray at ganymede.org> wrote:
>
> Hello -
>
> I am on a quest to learn more about how administrative boundaries can
> be managed as relations. I have a bit of experience with these
> things, but I am discovering the limitations of my knowledge also.
> Which was the point, actually.
>
> I would like to be able to suggest that governmental entities could
> manage their district geo data with OSM. I am interested in seeing why
> this does not work now and what can be done. Well, and it would be
> interesting to find out why so few cities in California actually seem
> to have a relation. Or perhaps I am missing it.
>
> I know that TIGER data was imported into OSM, but I am seeing some
> disconnects. To be precise:
>
> Using QGIS, I can load the vector files (SHP) from the following as two
> different layers:
>
> ftp://ftp2.census.gov/geo/tiger/TIGER2015/ELSD/tl_2015_06_elsd.zip
> ftp://ftp2.census.gov/geo/tiger/TIGER2015/EDGES/tl_2015_06085_edges.zip
>
> Using JOSM, I can see the "Sunnyvale East Channel":
>
> https://www.openstreetmap.org/#map=19/37.364537971457935/-122.02110206207291
>
> I cannot see how to get the id of this way from JOSM and its tag info
> seems to be:
>
> boat=no
> intermittent=yes
> name=Sunnyvale East Channel
> scvwd:FACILITY=2026
> scvwd:ROUTEID=20260
> waterway=drain
>
> And in QGIS, I can see the same feature (removing empty TIGER fields):
>
> wkt_geom        LINESTRING
>         -122.0213200000000171 37.36408999999999025
>         -122.02097200000001465 37.36464099999999178
>         -122.01992900000000475 37.36629399999999634
>         -122.01963900000001217 37.36675400000000025
> STATEFP 6
> COUNTYFP        85
> TLID    618169892
> TFIDL   229597201
> TFIDR   230278901
> MTFCC   P0001
> HYDROFLG        N
> RAILFLG N
> ROADFLG N
> OLFFLG  N
> EXTTYP  N
> GCSEFLG N
> OFFSETL N
> OFFSETR N
> TNIDF   39083667
> TNIDT   409312163
>
> But there seems to be no connection between the feature in OSM and the
> TIGER data. So, TIGER data was used to define new features? But perhaps
> TIGER id data was not merged onto existing features?
>
> I am certainly not seeing "tiger:tlid"="618169892" associated with this
> object in OSM anywhere.
>
> So, if I want to give the Sunnyvale District the relation that defines
> its boundaries, I cannot use TIGER data to find those lines? Or rather,
> I must use the TIGER data and find the line in OSM and set up the
> connection myself?
>
> Ok.... Any other suggestions?
>
> thanx - ray
>
>
> ps:
>
> My early stumblings are in my diary:
>
> http://www.openstreetmap.org/user/rayKiddy/diary
>
> Please excuse any ignorance on my part. I know a bit about the GIS
> practices of the state of California. I have a very small bit of
> experience with Santa Clara County. I have a smidgen of knowledge about
> the city of Sunnyvale. And I have more exposure to the Sunnyvale
> Elementary School District, having once been on the Board. And I
> develop database software and am interested in mapping applications.
>
>
>
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