Learn Italian: Il numero di turisti nella Spagna orientale va aumentando. - The number of tourists in Eastern Spain is increasing.

Normally, when you say you are in a country, you use the preposition in without a definite article, like in Spagna. However, because Spagna is modified by the adjective orientale (Eastern) here, the definite article is required. You combine in + la to get nella.

What is the difference between "va aumentando" and "sta aumentando"?

Both translate to "is increasing", but they have a slightly different feel. Using andare with a gerund (like va aumentando) emphasizes a gradual, continuous process over time, meaning "is gradually increasing" or "keeps on increasing". Using stare + gerund (sta aumentando) simply states that the action is happening right now.

Why is there no definite article before "turisti" ("di turisti" instead of "dei turisti")?

Here, turisti refers to tourists in a broad, undefined sense. Saying dei turisti would also be grammatically correct, but leaving the article out is very common and natural after expressions of quantity or measure, like il numero di (the number of) or un gruppo di (a group of).

Could I put the adjective before the noun and say "nella orientale Spagna"?

No, that would sound unnatural in Italian. Directional and geographical adjectives like orientale (eastern), settentrionale (northern), and meridionale (southern) almost always follow the noun they modify.