What role do physical barriers play in population distribution?

Physical barriers, such as mountains, rivers, and deserts, significantly influence population distribution by limiting or directing human settlement and movement. These barriers can create challenging conditions for people to cross, leading to the establishment of communities in more accessible areas. For instance, a mountain range may restrict migration or trade between regions, which affects where people choose to live and develop infrastructure. Conversely, areas that are easier to traverse, like plains or river valleys, tend to attract larger populations since they provide more favorable conditions for settlement, farming, and transportation. This concept explains why certain regions may remain sparsely populated while others become densely populated, shaping the overall landscape of human habitation. The other options, while they touch on important aspects of geography, do not capture the fundamental impact of physical barriers as controllers of where populations can thrive or struggle to thrive.