A Sphere is a 'bubble' of Aura that contains a volume of physical space.

Spheres exist in all sizes:
There are Spheres that envelop all of Alinsa, and Spheres the size of a palm.

Spheres are not spherical:
Most Spheres are somewhat rounded in shape for convenience, but have no limits on their geometry.

Multiple Spheres can occupy the same actual space:
It is common to be inside several Spheres simultaneously.
Entering the same space from a different location or Sphere can lead to different destinations.
The space inside of a Sphere can exceed, and is not tied, to the actual size or shape of the Sphere.