Without you having to give too much away about the actual location of your property on this forum you can look to see if the previous owners registered it at Basa. To do this go to www.goolzoom.com
On the drop down menu
Direccion - Poligono y Parcela
Provincia - Tarragona
Municipio - Ginestar
In the next 2 small boxes first put in your poligon then in the next your parcela number if you know it.  Then click the icon at the end
This should now show your land and if there is a small box on it that will be your property.
It should also come up with your Catastro number and if you click on it you can see what the Hacienda have your property down as.  I know they changed all the property registered with Basa to RESIDENTIAL - but they also did that to the ones with demolition orders on it so it still does not make it legal it only means they can now charge you residential tax.  Please do not think I am running the area down just stating the facts.
It you dont know your parcela number you can still locate it on the goolzoom map just look over Parcela 4 and you should be able to tell which is your plot.