The territories assigned to the ninety-one Parts are worth examining as a group, because their pattern says something about where the list came from.
They are, overwhelmingly, the geography of the classical authors. Ptolemy, Pliny, Strabo and Herodotus supply almost every identifiable name: Hyrcania, Sogdiana, Bactria, Oxiana, Colchis, Cappadocia, Paphlagonia, the Garamantes, the Nasamones, Coele-Syria, Commagene, Serica. These are not the names an Elizabethan would use for the world of 1584. They are the names in the books an Elizabethan scholar would have on his shelves, and Dee had one of the largest private libraries in England.
The distribution follows from that. The eastern Mediterranean, Anatolia and the Near East are divided very finely. North Africa is divided finely. Central Asia is unexpectedly well represented, tracking the route of Alexander's campaigns as the classical geographers describe them. Western Europe is treated broadly, with single Parts for Spain, Britain and Germany. India gets one Part. The Americas get none at all, ninety years after Columbus.
Several territories appear twice: Assyria, Bactria, Chaldea, Media and Idumea each occur under two entries in separate Aethyrs. The duplication is in Dee's own compilation and cannot be blamed on copyists.
And roughly a quarter of the names, Gosmam, Parsadal, Phalagon, Trenam, Onigap, Coxlant, Fiacim, Vinsan, Tolpam, Gorsin, Oacidi, Asnan, Adunia and others, match no known place at all. These have been read as regions unknown to Europe, as classical names garbled in transmission by ear, and as invention. The manuscripts do not decide it, and the honest description is that the list mixes a scholar's classical geography with a residue that nobody has been able to account for.