I guess I should explain this in a little more detail. The usage describes the cultures/languages in which the name is currently primarily used. If the name is no longer used, then it can be slotted into one of the "ancient" categories. If the name is only really used in literature (eg the Tolkien names) then it goes into the "literature" category. Likewise for the "mythology" and "biblical" names. If the name is only used to refer to a historic person, doesn't fit into one of the ancient categories, and isn't commonly used as a given name then it goes into the "history" category (eg Napolean, Attila). The "theology" category is reserved for a few select names that don't fit elsewhere.
Every other category should be self-explanatory. However, one note on the Welsh/Scottish/Irish categories -- Since a great deal of English names are also used in Wales, Scotland, and Ireland I am only classifying names as such when they are distinctively Welsh, Sco, or Irish.
Here's a list of the categories:
African New World Mythology Armenian Basque Biblical Biblical (Variant) Breton Bulgarian Catalan Ancient Celtic Ancient Celtic (Latinized) Celtic Mythology Celtic Mythology (Latinized) Chinese Judeo-Christian-Muslim Legend Croatian Czech Danish Dutch Ancient Egyptian Egyptian Mythology Egyptian Mythology (Hellenized) English English (Modern) Anglo-Saxon Anglo-Saxon (Latinized) Medieval English Anglo-Saxon Mythology Esperanto Far Eastern Mythology Finnish French Frisian Galician German Ancient Germanic Ancient Germanic (Latinized) Germanic Mythology Greek Ancient Greek Ancient Greek (Latinized) Ancient Greek (Anglicized) Greek Mythology Greek Mythology (Latinized) Greek Mythology (Anglicized) Hawaiian History Hungarian Icelandic Indian/Hindu Hindu Mythology Iranian Irish Irish Mythology Italian Japanese Jewish Khmer Korean Latvian Lithuanian Literature Manx Maori Muslim Mythology Near Eastern Mythology Near Eastern Mythology (Hellenized) Norwegian Pacific/Polynesian Polish Portuguese Provençal Romanian Ancient Roman Late Roman Roman Mythology Russian Scandinavian Ancient Scandinavian Old Norse Mythology Scottish Serbian Slovak Slovene Spanish Swedish Theology Turkish Ukrainian ? Vietnamese Welsh Welsh Mythology