Great article. The author explores, among many things and in a sensitive way, finding a closer approach to Dunbar's number.
One way to approach Dunbar's number which the author does not discuss is combining "special interest" with "local geography" as well. For example, you don't need to find a subculture of DIY telescope makers who only use brand X drive software and brand Y gearing; it used to be enough to be a DIY telescope maker within say a club of county scope -- e.g. DIY Telescope Makers of Ventura County. When that was the dominant approach, you weren't comparing your work to the best result to be found on Instagram in the last year.
One way to approach Dunbar's number which the author does not discuss is combining "special interest" with "local geography" as well. For example, you don't need to find a subculture of DIY telescope makers who only use brand X drive software and brand Y gearing; it used to be enough to be a DIY telescope maker within say a club of county scope -- e.g. DIY Telescope Makers of Ventura County. When that was the dominant approach, you weren't comparing your work to the best result to be found on Instagram in the last year.