Hi, thanks for commenting.

Before editing, I checked the guide on admin_level tagging to make sure I was doing the right thing. I ran into the exact same thing you quoted. However, this tagging seems rather inconsistent across Tokyo. Let's take one of the Nihonbashi quarters as an example:
relation/16187425

It has no chōme/字 but it was still tagged as admin_level=9. You might say that is erroneous tagging and should be fixed, but I disagree. They should all be tagged admin_level=9 because they're treated equally by the Statistics Bureau of Japan/統計局, regardless of if they have chōme/字 or not. I have a spreadsheet from the census open and it shows both 日本橋小舟町 and eg. 大手町 as「大字・町名」 It makes more sense for admin_level=9 to cover all of Tokyo, and to have gaps in admin_level=10, rather than having it be the opposite (because the 10s have to be a subset of the 9s, but that isn't possible with the current system). It might even be worth tagging some places which lack chōme/字 as both admin_level=9 AND admin_level=10 so that there's no gaps in either level. I'd be happy to talk more about it.

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Thanks! I found this island by mistake while looking for inspirations.