Why is Northumberland bordering England?

Hello, I am visually impaired and could do with some sighted help with a problem I have.

I have downloaded the relation for England id=“58447”

and the relation for Northumberland id=“88066”

I have written a program on my desktop that attempts to work out if relations border each other or are contained within each other. It generally works well but I am seeing an oddity where Northumberland is showing as bordering England and not being within England which I know it is.

The Northumberland relation turns out to be made up of 9 polygons. 7 of these, according to my program, are inside England. That is good. One polygon touches at a single node and one polygon is outside the England polygon. I am guessing one of the nine polygons is the mainland of Northumberland and the other eight are islands. But please is anyone able to put some eyes on this and explain why 7 of the polygons are inside England and one just touches and one is outside? I am struggling to find an approach to work this out myself.

Of course, it could be there is a bug in my program but it works so well in other areas I suspect there is something curious about the data I’m not catering for.

Many thanks for any help.

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Ce sujet de discussion accompagne la publication sur https://community.openstreetmap.org/t/why-is-northumberland-bordering-england/109697