Most people in Western Europe live within 100 miles of the coast primarily for reasons that involve trade and transportation. Coastal areas provide access to ports and shipping routes, which have historically facilitated trade and economic development. Additionally, proximity to the coast often means access to fishing and maritime industries, as well as freshwater resources via rivers that flow into the sea.
While factors like climate and natural resources (like good soil for farming, iron, and coal) do play a role in settlement patterns, the historical and economic advantages of coastal living—particularly related to trade and transportation—are the primary reason for the population distribution in Western Europe.