One of the best posts I've read about internet communities discusses this, long but worthwhile:

http://www.ribbonfarm.com/2010/12/07/socratic-fishing-in-lak...

The relevant point is the dynamic balance between "plazas" (highly accessible areas to anyone) and "warrens" (areas accessible only to an accultured in-group). "Evaporative cooling" is the phenomenon of the best contributing members "boiling off" and leaving due to frustration from excessive noise, flame wars, etc. From the post:

"Warrens are like rabbit warrens: low global visibility, highly personalized corners where small groups can aggregate/self-segregate. Plazas are like grand public town squares with lots of global visibility. Warrens are maze-like: it is hard to break out of your current corner, and it is easy to get lost. You couldn’t get lost in a plaza even if you wanted to.

[...]

'Warrenizing' a site undeniably slows evaporative cooling, by allowing groups to self-segregate. On Sulekha, we had a warren of individual topic boards, and a firehose plaza that consolidated the entire discussion stream at the landing page. When flame wars got too hot, we used to simply turn the plaza stream off, so people were forced to go directly to individual corners. Things would immediately get quieter. Groups would get sequestered, and therefore less likely to leave because of unpleasant activity elsewhere that they didn’t like."

What do you mean by "we" & sulekha. I used to be a regular almost a decade back. I used to make decent comments but used to put that one snide remark. Over a period I realised that distracted from the point I was making and no longer do that.

Over a period of time I learnt to ignore trolls and baits

I think that being able to shard the site into multiple subcommunities is a necessary but insufficient condition. Look, for example, at r/ShitRedditSays. The best you can hope for (above a community of a couple hundred) is people who will grudgingly use what you produce while talking about how useless it is.

I wonder if anybody has made a 'choose your own community' site. You choose how many people you're given access to (say, 100, 10K, 100K, 1M+) and the only information you get is from those who are nearest to you in location and interests (based on an adjustable scoring algorithm) and anybody you've previously conversed with.

Smaller communities could make for more specialized content, and everybody living on the edge of a bubble means theres plenty of opportunity for valuing middleman-style culture sharing (AKA reposts.)

Subreddits, right?

That's a little different...

Reading your post a few times, I don't really see the difference. Your last sentence perfectly summarizes small subreddits and cross-posts.

Reddit doesn't prevent more people from joining your sub. If you want a sub of 10K users, and 10M people join, too bad. Secondly, it doesn't filter users based on location. If I wanted to talk to the nearest 100 people, too bad. I have to make a new sub, find those people, and convince them to join.

So really, all of the two things that I suggested are things that reddit doesn't do.

It's very hard to bootstrap something that doesn't just let people add all their friends (from anywhere in the world).

A clique, a subreddit, a treehouse, a coffeehouse, a salon, a third place, a safe space, inside the magic circle...