How do we collect or define zones and regions in planning central ?

Summary

How do we collect or define zones and regions in planning central ?

Content

We have a requirement to see generated baseline forecast zone/ region wise. I understand this level of hierarchy is not present in planning central, but we can take care of through a custom report if we are able to attach customer sites to a region or zone. But I am not able to find where to define them. Any pointers appreciated.