GCP : Global, regional, and zonal resources

Some resources can be accessed by any other resource, across regions and zones. These global resources include preconfigured disk images, disk snapshots, and networks. Some resources can be accessed only by resources that are located in the same region. These regional resources include static external IP addresses. Other resources can be accessed only by resources that are located in the same zone. These zonal resources include VM instances, their types, and disks.

The scope of an operation varies depending on what kind of resources you're working with. For example, creating a network is a global operation because a network is a global resource, while reserving an IP address is a regional operation because the address is a regional resource.

As you start to optimize your GCP applications, it's important to understand how these regions and zones interact. For example, even if you could, you wouldn't want to attach a disk in one region to a computer in a different region because the latency you'd introduce would make for very poor performance. Thankfully, GCP won't let you do that; disks can only be attached to computers in the same zone.

References:
https://cloud.google.com/docs/overview/