A raid can trigger when you're in an area with at least three "base structures", which include portals, tables, workbenches, and campfires. The other day I had a dwarf raid in the middle of a forest just because I had set up a campfire along with a temporary workbench + portal to go sleep at home.

You do need to be within the red circle for the raid to end. I left that dwarf raid because I wasn't interested, so it stayed there for numerous days, until a raid triggered at my base and erased the forest one.

(The wolf hunt event is an exception to both of these, I believe.)