http://www.mapa.es/es/sig/sig1.htm
Then you have one of four options. I always use the oleícola link, but I guess the last one - SIGPAC - is probably as good or better.
You will need Internet Explorer as you have to download a plugin that doesn't seem to work in anything else.
You will also need to understand Spanish and know your polygon and parcela numbers.

I'm experimenting with SIGPAC at the moment and you don't need to download anything. In fact it's very good. The aerial photos are frightening.

Search for your location by clicking on the binoculars icon at the top, then select progresivo from the menu, then fill in the details: Cataluña, Tarragona etc.

It seems a little flaky, but that's probably my connection.

Good luck,

Leo