Final answer:
The largest city south of the 46th parallel is São Paulo, Brazil, with a population exceeding 20 million. It is the most populous city in the Southern Hemisphere and a global hub for business and commerce.
Step-by-step explanation:
The largest city in the world south of the 46th parallel is São Paulo, Brazil. This city is not only a regional powerhouse but also a global city that plays a central role in international business, commerce, finance, and the arts.
Despite its inland location, approximately 30 miles from the coast, São Paulo grew significantly due to its early economy based on coffee production and has now evolved to become the center of trade and industry in Brazil.
With a population exceeding 20 million residents, it stands as the most populous city in the Southern Hemisphere, making it larger than other major South American cities such as Rio de Janeiro and Buenos Aires.