assuming you mean an area in a 360° spherical video that is not covered by cameras, it is really dependent on your shooting set up, how many cameras, focal length, rig configuration, parallax issues etc
freedom360 gopro mount has a very minimal to non existent blind spot where the rig attaches to pole, other options might have a larger dead zone not covered by camera which might be hidden with a nadir logo etc
http://freedom360.us
sam