Yes it is dependant as per my understanding, although I am not very experienced. The value of BTC increases when there is more investment and more people are buying BTC. Usually it is measured in Dollar because it is one of the famous and powerful currency in the world, but you can select your own currency if dollar is not your currency. There are a lot of options in coinmarketcap.com
You have a point, but an a certain part even though we dont actually see it, Bitcoin is sort of related to fiat. Local currency or fiat is a reflection of a country's economic state, and if it was not good as what it should be will affect the current state of fiat,which will tend to the investors to lessen the amount of the investments that they should commit which will definitely the cryprocurrency.