You are asking a meaningless question here, bit the answer is easy, you are measuring ownership of a scarce resource.
I question the legitimacy of bitcoin being a real resource. Furhermore, the number of total bitcoin may be somewhat scarce, but the fact that it can be acquired by anyone who wants it means it is not really scarce, and the price people are willing to pay for it makes it less scarce as it is easily divided into fractions of a bitcoin.