Map of South America Rivers
If you are traveling anywhere in the world, pay attention to the rivers.
The rivers were the first form of transportation, then the road, or trains,
so normally most cities are built along rivers for fresh water and
transportation, then come the road, and sometimes trains in South America,
however not really.
Therefore if you understand the rivers of a continent you start to
understand separations of culture, mountains, languages and how it evolved
to the present conditions, there are natural boundaries in the world.