Hi, Neil. Here in the Comunitat Valenciana it's even messier, as municipalities can opt to have either the Spanish or Valencian form as their 'official' name. Or both. Which means there is no single definitive linguistic version for cartographical database purposes.

I live in La Nucia, which is officially referred to as such in Valencian, with no accent on the 'i', whereas in Spanish it would be La Nucía. So when anyone calls from elsewhere in Spain and reads out the address, they pronounce it as La Nucia, rhyming with 'astucia', rather than 'Lucía'.