The Land Registration Office gives security to the purchase against a third party. The documents come from a Notary Office or the decisions pronounced by a Court. Only a notarized deed will go into the Land Registration Office.
Frequently, a private contract is made and then, in the Notary Office, the descriptions are different; boundaries are registered but it is necessary to find out the present adjoining parts to be registered in the new deed. The notarized deed is the really important, as it is the document which will go to the Land Registration Office.
The Cadastre is a register of the Ministry of Economics made for tax purposes in order to pay the tax of Personal Property (IBI). Nowadays, the Notary Office passes the information of the purchases to the Cadastre in order to be updated. Some years ago it was not like that, so it is sometimes convenient to do an updating of the cadastral data.
The Cadastre does not generate civil rights on the property, unlike the Land Registration Office, which bears witness to the authenticity of the documents.
Galicia is a region with properties of small holdings, so it is possible to find mistakes in the Cadastre. That is why is convenient to adapt the reality to the purchase, so as to the Cadastre and the Register are concordant.