geocodejson output: make sure a level is only printed once

[mtmail]

Another fix to #3382

Example:
curl 'https://nominatim.osm.org/reverse?lat=51.01762378&lon=-3.1520338&format=geocodejson' prints
[...]"admin":{"level10":"Bishop's Hull","level10":"Bradford-on-Tone","level6":"Som[...]

Browsers and Nominatim CLI handle duplicate keys by selecting the last occurrence ("Bradford-on-Tone") while the fix I added selects the first ("Bishop's Hull").

https://nominatim.openstreetmap.org/ui/details.html?osmtype=W&osmid=6011967

[lonvia]

I don't think this is about first/last occurrence. We have a street here that goes through two admin_level=10 areas. You'd probably want to select one were the majority of the road is. Or for a house number, you'd want to select the one, it is actually in. It would be relatively expensive to do such a computation on admin_level level.

While I see that there is potentially a problem here, I'd file this particular example under data issue. Bishop's Hull is mapped as a suburb and even tagged with is_in=Tauton but the administrative boundary for Tauton disagrees and excludes Bishop's Hull. The result is that Bishop's Hull is a suburb without a city to be in. Upgrade Bishop's Hull to village and all is well.

[mtmail]

Thanks for pointers. Fixing the OSM data worked.

I saw a lot more places where this is happening but I'll keep the code fix in my local installation. We can review when somebody else reports the same issue. Probably my JSON parser (Perl) isn't modern enough.