I noticed that several districts of Moscow have unexpected feature codes. I would expect them to be PPLX (section of populated place). And most of them are, but there are several exceptions.
As the districts also have administrative functions and a corresponding ADM3 feature exists it is not wrong to consider them a ppla3.
When a feature has several functions (like ppla and pplc at the same time) then the more relevant one is used. From this point of view it is correct to have them as ppla3.
Thanks for your answer. I can understand your point of view. It's just that in this case, all districts should be PPLA3. Because they all have this function. But they are all part of Moscow, so they almost all have PPLX. But I see it's actually the same way for other cities like New York (Brooklyn, Queens etc are PPLA2).
But in general I can see there is no clear line at the moment. For example also in New York, Harlem is a PPLX, but East Harlem is a PPL.
Maybe there is a better way? Basically, what I wanted to achieve is to distinguish "actual" cities from districts/neighborhoods of a city. But this looks impossible to do based on their feature codes.