It may be an idea to submit an official “SOLICITUD DE CERTIFICACION CATASTRAL” in order to get the most up to date Catastral plan. Over the past years in Spain there have been moves to update records and this may not have fed through to the Land Registry.This form can be obtained from the Catastral office which deals with your area. For instance I submitted ours to the Alicante office for a house and land in Altea. There are 3 types of documents you can obtain and the one you should request is the “Certificacion Descriptiva y Grafica”.
If you let me have a fax number I can send you a copy of our request form so your lawyer or architect can help you with it.
Another alternativve is to ask for a legally agreed and defined boundary survey if the adjacent owners involved are not currently in agreement. Your lawyer and architect should be able to advise you on how this is achieved.
I know it may sound time consuming and complicated but one of the oldest problems in Spain with regard to property is that the Land Registry details very rarely matched the catastral plans. The former were used for ownership purposes with the latter merely used for tax calculation purposes. We had a similar problem for years on Fuerteventura and only in 2003 did we actually get the local catastral office to issue details which matched those referred to in the Land Registry.