Why is Spain divided into 5 geographic regions?

Spain is actually divided into 15 geographic regions. These regions are:

* Andalusia

* Aragon

* Asturias

* Balearic Islands

* Basque Country

* Canary Islands

* Cantabria

* Castile-La Mancha

* Castile and León

* Catalonia

* Extremadura

* Galicia

* La Rioja

* Madrid

* Murcia

* Navarre

* Valencia