şehridir. >> şehirdir. [?]

Correct as is.

şehirdir = #1806372

''New York dünyanın en büyük şehridir.'' means ''New York is the world's biggest city.''

Thank you. I'm studying Turkish, and I didn't know that "şehirdir" = "şehridir".

Now I see:

dünyanın... şehri

dünyada... şehir

No, "şehirdir" is not equal to "şehridir"

This is a pencil. = Bu kalemdir.
This is her pencil. =Bu onun kalemidir.

London is a city. = Londra şehirdir.
London is a city of England. Londra İngiltere'nin şehridir.

New York is a city. = New York bir şehirdir.
New York is a big city.= New York büyük bir şehirdir.
New York is the biggest city. = New York en büyük şehirdir.
New York is the biggest city in the world. = New York dünyadaki en büyük şehirdir.
New York is the world's biggest city. = New York dünyanın en büyük ''şehridir.''

It's good to hear that you study Turkish. I'd be glad if I can be of any help to you.

As I said, I now understand. In Turkish, we have "possessor ending" [-in] and "possessed ending" too [-i].

So, in "New York dünyanın en büyük şehridir." we have:
possessor ... dünyanın (of the world)
possessed ... şehri (city) >> şehir + -i = şehri

[N. Y. is the biggest city of the world.]

But in "New York dünyada en büyük şehirdir." we don't have a "possessing relation", if I may say so:

dünyada ... in the world
şehir ... city

[N. Y. is the biggest city in the world.]

Right?

Right.

Dünya+n+ın şehr+i (which is actually şehir+i but first ''i'' drops and it becomes ''şehri'')

<<<
But in "New York dünyada en büyük şehirdir." we don't have a "possessing relation"
>>>

Yes, there is no ''possession'' in that sentence.

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By the way, ''in the world'' = ''dünyada'' and ''dünyadaki''
Both are correct but I prefer the second one. It sounds better to me.

Thank you very much!

dünyadaki = in the whole world [?]

''Dünyadaki'' is anything that exists in the world.

Books in the world = dünyadaki kitaplar, animals in the world = dünyadaki hayvanlar, languages in the world = dünyadaki diller

You cannot say ''dünyada diller, dünyada hayvanlar, or dünyada diller'' if you want to mean something that is in the world.

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''Dünyada'' is used when you say something which happens in the world.

People are living in the world. = İnsanlar dünyada yaşıyor.

whereas

People in the world have their own personalities. = Dünyadaki insanların kendi kişilikleri vardır.

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It may be a bit extreme but:

People in the world have their own personalities in the world. = Dünyada, dünyadaki insanların kendi kişilikleri vardır.

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''Whole'' doesn't change anything. You just add ''bütün'' before ''dünyada'' or ''dünyadaki''

You may now think that ''New York dünyada en büyük şehirdir.'' is incorrect since it's not ''dünyadaki''

''Dünyadaki'' would be better but both are correct in daily life.

OK. Thanks a lot!