That’s not true? the urban extent of Paris has continuously expanded and now covers 3000km2

Officially most of that is not Paris

And London is just ‘the city of London’ . The continuously built up area of a city is a useful definition for these reasons! Administrative boundaries commonly make no sense!

Right but they both reflect and shape where people think the city limits are. And for administrative purposes it matters that, whatever locals may think, Dulwich is officially in London but Montrouge is not officially in Paris