That list does not make much sense, because it mostly consists of small municipalities that have been engulfed by growing metropolitan areas. Four of the five Spanish entries are like that, three in Valencia and one in Barcelona; and most other entries in the top 20 are suburbs of Paris, Athens or Naples.
> A city proper is the geographical area contained within city limits
I'm not sure about the others, but the one from Barcelona is a city actually, with their own local government and all, separate from Barcelona, exactly like Badalona on the other end of Barcelona. It is within the city-limits of Barcelona (region, not city) though.
It is, but my point is that these entries are more historical oddities than a sign of particularly high population density of Spanish cities. There are similarly dense suburbs in most cities/countries, they just happen not to have a local government.
That list does not make much sense, because it mostly consists of small municipalities that have been engulfed by growing metropolitan areas. Four of the five Spanish entries are like that, three in Valencia and one in Barcelona; and most other entries in the top 20 are suburbs of Paris, Athens or Naples.