Large disturbance is a kind of safety & incidents issue you might spot in your area. Narks lets you flag it anonymously on a shared map so others nearby can see what is happening and corroborate reports that are still active. Reports decay over time unless other users confirm them, so the map always reflects what is relevant right now.
If you would call what you are seeing “large disturbance” — and it is happening right now at a specific location — it belongs here. Recent reports from other users near you appear on the map when you open Narks.