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One third of the population of Switzerland lives within 5 kilometers of the main train line crossing the country
(reddthat.com)
Source (yes sorry it's LinkedIn, if you any another one, I'll update): https://www.linkedin.com/posts/prof-stefan-michel_notsweden-train-activity-7210174690827370496-8iJz?utm_source=share&utm_medium=member_ios
You’re absolutely right. That train runs across the Swiss Plateau with mountains either side of the plateau. Historically, if you were going to grow any produce, that was where you would grow it so it’s no surprise there’s such a density of people in the flatter part of an extremely mountainous country.