Best I can tell is that Sao Paulo ended up number one because the Brazilian coffee boom was centered there, which meant it had the wealth to industrialize and ride that wave. Its dominance was solidified after Rio de Janeiro got kneecapped by the capital moving to Brasilia.
Depends on what you call the city. This is surely the one mayor only, which is perfectly legit. However, if you talk about a metropolitan area, NYC is the largest in area and money.
