Did you say that each zone is a logical group of data centers? In AWS, one AZ is one data center (physical building). Does Google got multiple data centers in each zone?
The above question is in reference to GCP design and structure lesson in chapter # 3.2
AWS can have one or move Datacentres in a single AZ which is nicely discussed in below thread.
Also, GCP follows a similar kind of pattern and a zone can have more than one physical building or data centre to form a zone.
I could not find a GCP doc to back up my answer but this is another reference.
Hope this helps.
This document might be helpful: https://cloud.google.com/compute/docs/regions-zones
The document states: "Compute Engine implements a layer of abstraction between zones and the physical clusters where the zones are hosted. A cluster represents a distinct physical infrastructure that is housed in a data center."
The document goes on to say that "Each zone is hosted in one or more cluster."