Overpass: find relations that have no members with a particular role

Question

How do I make a query that returns me every admin_level=7 relation in Poland that doesn't have a member with admin_centre role?

This is a pre-requisite to another thing - After fixing these (if needed, I wanna find out) I want to list every place in Poland that should feature amenity=townhall, but has none. This is what I've got currently: http://overpass-turbo.eu/s/dJo

~~In this second query I also have to solve a problem: Some rural municipalities have their seat outside them, how do I exclude these? cf. https://en.wikipedia.org/wiki/Gmina~~

Accepted Answer

I will focus on your first question atm. If possible, please move your other question to dedicated threads.

Here's how the query should look like

[timeout:600];

area[admin_level=2]["name"="Polska"][boundary=administrative]->.boundaryarea;

( rel(area.boundaryarea)[boundary=administrative][admin_level=7]; -

  ( node(r:"admin_centre")->.a;
    rel(bn.a)[boundary=administrative][admin_level=7]; 
  );
);

out geom;

Overpass Turbo Link: http://overpass-turbo.eu/s/dLT

A few words how this works:

We initially get a boundaryarea as defined per Poland's admin_level=2 boundary
Now we determine difference of all admin_level=7 boundaries in that area MINUS those admin_level=7 boundaries having an admin_centre node.

Read more about the recurse functions used in this query here.

Note that there are some relations returned outside of Poland. This is not a bug in the query, but rather some outdated areas on overpass-api.de. See this thread for details. It works just fine on our dev box with up-to-date areas.

Overpass: find relations that have no members with a particular role

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