[Talk-GB] Administrative boundaries: polygons or polylines?

Colin Smale colin.smale at xs4all.nl
Sun Jan 17 17:45:25 UTC 2016


Hi Bob, 

I have been doing a lot of work looking after admin boundaries in the UK
in the last few years, including adding many thousands of Civil Parish
relations. 

Admin boundaries are represented by relations with type=boundary.
Syntactically these are similar to multipolygons, whereby the (one or
more) "way" members have to link up to make (inner or outer) polygons.
Even an isolated parish (an island for example) which only needs a
single way to represent its entire border, would still have a boundary
relation in OSM.

How are you distinguishing between boundaries as polygons and boundaries
as polylines? 

//colin 

On 2016-01-17 18:30, Bob Hawkins wrote:

> While running an Overpass turbo query recently I noticed a mixture of polygon and polyline admin_level 10, civil parishes in South Oxfordshire within the bounding box, but mostly polylines.  Its neighbour, South Buckinghamshire, appears to contain civil parish polygons.  I checked other, random parts of the country.  Canterbury, Crewe, Norwich and Plymouth areas comprised polygons.  I did find Kingston upon Hull area, probably created by Chris Hill, comprised polylines.  I was responsible for work on admin_level 10 boundaries within South Oxfordshire four years ago and creating a relation for each one (Chris gave me much advice and assistance to help me carry out these tasks).  The relation alone can be the polygon, it seems to me, for an administrative boundary comprises many lines because they are shared with adjacent boundaries and because of other unassociated coincident tags. 
> I am interested to know the following: 
> how Overpass turbo distinguishes the two types 
> which type civil parishes should be and whether the same applies to all administrative levels 
> how an administrative boundary is determined to be a polygon or polyline and is created in the first instance, how this is seen in JOSM, for example, and how to change from one to another, assuming civil parishes should be polygons, based on the majority I have seen 
> I appreciate spatial queries such as "admin_level 7 contains admin_level 10" or "prow_ref [tagged Public Rights of Way] within admin_level 10", for example, would require those boundaries to be polygons.  In this regard, is it possible to carry out such spatial queries in Overpass turbo? 
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