Final answer:
São Paulo is the largest city in the Southern Hemisphere, boasting a population surpassing 20 million and standing as the industrial heart of Brazil.
Step-by-step explanation:
The largest city in the entire Southern Hemisphere is São Paulo, Brazil. Founded in 1554, São Paulo started as a small mission and has since grown into an immense urban metropolis, becoming the heart of the core region in Brazil. With a population of more than 20 million, it is not only the largest city in the Southern Hemisphere but also the largest industrial metropolis south of the equator and the largest city in South America.
São Paulo's economy historically flourished due to the coffee production and has evolved to be Brazil's center of trade and industry, outpacing other significant cities such as Rio de Janeiro and Brasilia in terms of industry, despite Rio being a more popular tourist destination.