There are many planes of existence in the Cityverse, some very like our own, and some very different. All contain essentially similar physical properties, though they vary in structure and content.
There are two types of pages: prime pages and realm-shards. Most prime pages have a single sentient being type that dominates that realm. The Plane of Earth, for example, has only one original being type: two-legged, two-armed humanoids close in appearance and power to Humans. Vastly different types of creatures exist on the same page, but the great majority of them do not have the soul-spark.
Known independent pages:
The Plane of Earth
Known independent realm-shards: