Final answer:
Most South American population centers are located near or at the coast because of the export-oriented colonial economies which utilized the coasts for trade, and because inland areas were often less hospitable for settlement and agriculture.
Step-by-step explanation:
The reason most South American population centers are located near or at the coast traces back to historical and economic reasons. During colonial times, the economies of South American societies were heavily export-oriented. They were engaged in the Atlantic Trade Triangle, which was an efficient means to transport goods, slaves, and crops such as sugar and tobacco, necessary for the economic prosperity of the colonial powers. This export-oriented economy necessitated the establishment of ports along the coast to facilitate the shipping of goods. Moreover, coastal areas often provided more favorable conditions for agriculture, like in the Guianas where plantation agriculture thrived due to the easy access to trade routes and the availability of forced labor.
In addition to these economic factors, geographical aspects also played a role. Much of the inland areas of South America have challenging terrain, such as rainforests, highlands, and in some areas, arid conditions, which made them less hospitable for large-scale settlement and agricultural activities compared to coastal regions. The coastal cities were thus naturally preferred for their accessibility and the ability to sustain large populations, leading to them becoming the primary urban centers.