[cross-posted]

FYI:

https://rcahmw.gov.uk/mapping-the-historic-boundaries-of-wales-commotes-and-...

"The Royal Commission [on the Ancient and Historical Monuments of Wales] has developed two digital geospatial layers using late-medieval sources and historic parish boundaries to recreate the boundaries of the commotes (cymydau) and cantrefs (cantrefi) of medieval Wales."