With radius 1. A kind of unit of area, different from human units for area (eg square kilometers, acres, etc). Compare Area =πr(squared) for a circle to Area for a square = side(squared) we see a more "efficient" coverage of an area - by factor π.
it is interesting that ancient iconography often used orbs or spheres to represent angels or angelic influence. And not areas with angled boundaries.
Here the Archangel Gabriel at the Annunciation before the Blessed Virgin Mary.