From the reservation you sign on a Tuesday to the notary, the registry and the bills that follow — the points in an island purchase where the number is genuinely needed.
Island purchases move in an odd rhythm. Buyers often see three properties in a long weekend, reserve one before flying home, and then spend the next two months waiting on documents from a distance. That gap is where the identification number belongs, and where it is most often forgotten.
The reservation stage is usually informal in feel and binding in substance. A holding deposit takes the property off the market; a private contract with a deposit clause follows and sets out what happens if either side walks away. Nobody asks for a number at that point, which is exactly why it slips down the list. By the time the deed is being drafted, it is not optional, and a rushed request is a stressful one.
Due diligence is the stage that repays patience. A land registry extract shows who owns the property, what charges sit on it and how it is described; the community of owners can tell you about outstanding fees and planned works; the town hall holds the local property-tax position. If any part of your plan involves letting the place to holidaymakers, treat that as its own investigation entirely — tourist-letting rules in the Canary Islands are administered separately, they have changed more than once, and a lawyer familiar with current Canarian practice is worth more than any assurance from a seller.
At the notary, identification is the whole point of the exercise. Everyone who will appear on the deed generally needs to be identifiable to the administration in their own right, so a couple buying together are two files, not one. If you cannot be on the island on the day, a power of attorney is the normal answer, but it needs drafting and legalising in advance, and the wording has to cover what the notary will actually be asked to do.
After signature the work continues quietly. There are transfer taxes to file within set periods, the deed to inscribe at the property register, utility and rubbish accounts to move into your name, and the annual local property tax to set up by direct debit. Owning a home here also brings its own tax reporting for non-resident owners, whether or not you ever let it out — the specifics depend on your circumstances and are a question for a tax adviser, not a forum.
One point deserves emphasis because it is misunderstood so often: buying property in Spain does not make you a resident, does not grant any right to live here beyond the terms of your visa or nationality, and does not change your tax residence. The number identifies you to the administration. Everything else is a separate question with a separate answer.
Finally, allow for the geography. Ferries and short flights connect the islands, notaries and registries keep their own hours, and a document that needs signing in person is harder to arrange from Fuerteventura than from a mainland city. Build slack into the timetable, keep every reference number, and have a qualified professional — or the official channel itself — confirm how each step stands before you commit to a completion date.