I believe it’s 100 miles from the border including coastlines but does not include a 100 mile radius around international airports. I don’t remember the source but Ive seen a map that represented it that way.

Also worth noting, this ruling only benefits citizens in that specific district, as other districts aren’t bound by its rulings. Personally I’d recommend having a 2nd device you can use to record your interactions because if they violate your rights your chances of getting their body cam video of it aren’t great.