This conversation has kind of sucked from the get go, and has been almost not worth participating in, because the original list (like most lists of this sort) never corrected GDP for purchasing power, and is therefore meaningless. A lot of the arguments in this thread boil down to that confusion. Nominal GDP in US dollars means nothing in countries that
don't use US dollars.
What matters for everything we actually care about in our conversations on this happy little website (living standards, military capability, the ability to build infrastructure... skyscrapers... etc) is actual economic activity; what is actually happening and being produced on the ground in a particular place.
Just think about it for a second (using a deliberately extreme thought experiment): imagine a country with no people, and an entirely robotic supply chain. The only things it imports are raw materials and the only things it exports are extremely cheap finished goods (cheap because, again, there is no labor in this country. Also it is powered totally by renewables). The whole country is just one giant vertically-integrated factory. All the following prices are in 2026 US dollars. Per year, this country/factory makes 1 million electric cars (which cost $200 each), 10,000 5th gen fighter jets (which cost $10,000 each), and 1 million FPV drones (which cost $50). Using these numbers, this country would have a nominal GDP of... $350 million. But if we wanted to produce all these same things in the US in 2026, at current prices, we would require at least 5,000 (probably more like 10,000) times more dollars to change hands, because our economy is
significantly less efficient than this hypothetical economy. Put more succinctly: we are
worse at production than this country, so producing the same things as them is more costly for us. Do we see the problem now?
The best measure (one of the ONLY non-— measures) we have of actual aggregate economic activity is GDP at purchasing power parity (PPP). Here is the list of countries by GDP@PPP:
https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(PPP).
As you can see, this list looks a little different than the list we often see. China is already by far the world's largest economy, and Russia is the 4th.
With that out of the way... back to the topic of city economies
Speaking of Russia, Moscow is always severely underrated on all these types of lists for political reasons (why do we do this? its so childish). As the primate city of one of the world's largest economies, and with a metro population of over 20 million, Moscow has a massive economy. At purchasing power parity (rubles to dollars), the Moscow metropolitan economy is somewhere around $1.8 trillion, and is growing despite (and to some extent because of) the war. If you then correct for the fact that Moscow is more expensive (30-40% more expensive) than Russia on average, then the number shrinks to about $1.35 trillion.. just a bit smaller than the economy of the LA area.