> That's why there is an advert for ADT or Ring at the top of every feed, every day.

can't speak to this, as I use adblock when browsing. I don't doubt you, though.

> That's why crime posts are distributed to your whole city while general posts default to your neighborhood.

I don't see this. first of all, I don't actually see a specific "crime" category, presumably this falls under "safety". if I try to add a post to a specific category, I don't notice any difference in the default settings.

as for what I see in my home feed, I only see crime related posts from users in nearby locations (ie, my neighborhood and immediately adjacent ones). I only see city-wide posts from city officials, and these are on a variety of topics.

I can't verify this any more because I spiked my Nextdoor account by "moving" to Comiskey Park, but when I used it "Crime & Safety" was one of the top-level categories under which you could post, along with General, For Sale, etc. When you chose Crime & Safety, the maximum scope to which you could post was broadened to include your whole "wider area" which for me was all of central and north Oakland, Piedmont, and Alameda.

  the maximum scope to which you could post was broadened to include your whole "wider area"

This works the same for all categories, even For Sale and Free.

  That's why crime posts are distributed to your whole city while general posts default to your neighborhood.

That's false.