I've been studying kanjis for the JLPT and I still can't understand when 区 is used. The textbook only said that that kanji means area but it doesn't have examples. I found one like this on the internet:
- 東京23区
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Sign up to join this community区 is translated as ward. 東京23区 are the core 23 special wards in Tokyo Prefecture, which do not belong to any 市町村 (city, town or village). Some large cities in other prefectures also have 区 as subdivisions of 市.
See:
EDIT: 区 can also refer to a subdivision of a city in many foreign countries. Such subdivisions are called under various names, but 区 is the kanji generally used in Japanese.
When used in a compound, it can have even broader sense (区域 is "district" in general).