Shanghai's Urban Area is still the largest in China. If you take Metropolitan Areas, then Guangzhou, whose Metropolitan Area swallows up nearby Shenzhen (pop 12 million), would be considered the largest.
An interesting one with South Africa's 3 capitals, which are zero, 367 and 1263 km from Johannesburg. (The "zero" is if you accept citypopulation.de's view that Pretoria is a part of Johannesburg, but from city centre to city centre, you're looking at around 50 km). Will put that as a note into the instructions.
Katowice is not the largest city, there is only a conurbation of more cities in that region, but each of them is governed separately. That one is definitely wrong.
The description needs to clarify if you are referring to city proper versus metro area and you need to be consistent. Sometimes you are referring to urban areas (Katowice) and sometimes city proper (Mumbai versus Delhi).