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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