I won't comment on the scientific merits of this article, just thought it was an interesting viewpoint.
https://www.vox.com/platform/amp/201...ult-friendship
From personal experience, the idea about spontaneous encounters being conducive to forming friendships has a lot going for it. When I moved to this town, from sthlm, the greater exposure to spontaneous encounters--both deliberate and completely unintentional--was key to forming lasting friendships. I now live in a part of town slightly less suited to such encounters, but they continue in the hospital, on walks to town etc. It's a lot more pleasant and social than living in a city where all movement outside the home is purpose-driven.