After the latest administrative reform in Estonia this standard is Et:Key:addr:* - OpenStreetMap Wiki is quite confusing. After some Maa-Amet imports (2019 and later) there now are two contradictory ways how data is presented.
one way (this causes that an address can exist several times in one municipality)
Way History: 227116937 | OpenStreetMap Haapsalu (omavalitsus) and not Herjava küla (asustusüksus)
Way History: 212577429 | OpenStreetMap Pärnu (omavalitsus) and not Tõstamaa alevik (asustusüksus)
Way History: 213320412 | OpenStreetMap Tartu (omavalitsus) and not should be Haage küla (asustusüksus)
Way History: 226686494 | OpenStreetMap Lihula (asustusüksus) and not Lääneranna vald (omavalitsus)
Way History: 213731770 | OpenStreetMap Sauga alevik (asustusüksus) and not Tori vald (omavalitsus)
There are no good solutions, but proposals could be:
- for new megamunicipalities start using addr:district (addr:city=Haapsalu and addr:district=Herjava küla)
- or find something else from here Key:addr:* - OpenStreetMap Wiki to fit the way how Maa-amet ADS is defined (old “Pärnu maakond, Tõstamaa vald, Tõstamaa alevik, Varbla mnt 10” to new “Pärnu maakond, Pärnu linn, Tõstamaa alevik, Varbla mnt 10”)
- keep the old way of addr:city meaning asustusüksus and all other relations can be found from there (this would be the easiest to implement and carry on how Estonian OSM has worked for 15 years) and this is also in correlation with this statement “Municipality (Kohalik omavalitsus) names are not given, this can be taken from level admin info, e.g. Nominatim finds it from it nicely.” from Et:Key:addr:* - OpenStreetMap Wiki but there are two hardcoded exceptions (Tallinn and Kohtla-Järve, where “addr:city means city proper”)
I would suggest to carry on as it has been before megamunicipalities (i.e. proposal 3) and I have followed this practice “addr:city means asustusüksus” (with two hardcoded exceptions (Tallinn and Kohtla-Järve, where “addr:city means city proper”)).
Please note that for example “Kase 4” exists both in asustusüksus “Haapsalu linn” and “Herjava küla”, but both are in the same municipality “vald - Haapsalu linn”. And in real life they are just 3 km apart. So only “addr:city means asustusüksus” is a working solution.
If we should go for “addr:city means vald”, then for exaple we need to rename all addr:city in Saaremaa and Hiiumaa (as both have on municipality covering whole island) and that would be very strange.
I actually wrote about this to @SviMik (main importer at that point in time) and got a response as well. However without his explicit approval I probably can not publish it here.