Final answer:
Fact 2, which states that population density in Australia is affected by a large desert, is most closely related to why cities along coasts have higher population concentrations.
Step-by-step explanation:
The high concentration of people in coastal cities can be explained by various agglomeration factors, including economic opportunities, access to trade and transportation, and availability of resources. Among the provided facts, Fact 2: In Australia, population density is affected by a large desert is the most closely related to population concentrations in coastal areas. This indicates that geographical features can significantly influence where populations settle and underscores why cities along coasts are often more densely populated than interior regions.