Eivissa is Ibiza.
Castillian Spanish is the language of the Spanish Government in Madrid and the Spanish you learn if you take a Spanish course abroad. However many regions have their own individual languages and dialects. Ibiza is no exception.
The official language of Ibiza is Catalan. All road signs use the Catalan names for each village and beach. For example Ibiza becomes Eivissa; San Antonio becomes Sant Antoni. Here is list of the more common names with their Catalan equivalents:
Ibiza: Eivissa
San Antonio: Sant Antoni
Santa Eulalia: Santa Eulària
Es Caná: Es Canar
San José: Sant Josep
San Rafael: Sant Rafel
San Jorge: Sant Jordi
San Miguel: Sant Miquel
Santa Ines: Santa Agnes
Playa d'en Bossa: Platja den Bossa
Playa de Las Salinas: Platja de Ses Salines
Cala Conta: Platjes de ses Comptes
Although we use the Castillian Spanish names in all of our maps and texts, we have added the Catalan name where appropriate in brackets to help you when out and about in Ibiza. But as you can see most Catalan names are similar to the Castillian ones so you won't have any problems.
Interesting Fact:
The locals do not actually speak true Catalan, rather they speak a Catalan dialect called Ibicenco (Eivissenc). Valencia and Alicante also speak Catalan dialects called Valenciano and Alicantino.
The Ibicenco of the North in villages such as San Mateu or Santa Agnes is noticeably different to the Ibicenco of La Ciutat de Eivissa (Ibiza Town).
Dalt Vila really means high town, not old town as one might suspect!