Level
Brain
Every region of the atlas, nested as the ontology nests them
Viewport spans 12.0 mm
The structure
A brain is divided into structures that CONTAIN one another rather than sitting side by side. The mouse atlas nests 1,327 of them under a single root: grey matter divides into cerebrum, brainstem and cerebellum; cerebrum into cortex and nuclei; cortex into areas; areas into layers. Each point here is one structure, placed at the centroid Allen computed for it in the P56 reference space, coloured by Allen's own scheme, and sized by how deep in that hierarchy it sits — so the coarse anatomy reads first and the detail fills in.
Source
Allen Institute structure graph
Points, not volumes. Drawing 1,327 nested shapes needs the annotation volume, which is hundreds of megabytes. This is an honest map of WHERE structures are, not a rendering of what they look like.
Atlas
These are separate ontologies in separate coordinate spaces, with no correspondence between their structure ids. Switching is a jump between atlases, not a zoom.