Why do we address Unguja.cz, but the page is called Zanzibar.

Unguja is Swahili for the designation of "our" Zanzibar, a large southern island of the archipelago "Zanzibar Archipelago", which covers more than twenty islands including Pemba. Zanzibar is to take a colonial term for this island, and is present in almost all European Atlas.
Zanzibar also known by the largest city Unguji. Well, it should be called Unguja Mjini English or Zanzibar City.

Zanzibar word comes from Arabic. Zanzibar could be translated as black country (Zijn el-Barr). It was used by Arab traders from the 8th century Zanzibar archipelago and adjacent mainland. Later, the name began to use the Portuguese (Zanquebar) followed by English as Zanzibar. Then add the other.