Dia is in Gualta. Tap the map or the "Get directions" button to see the exact location and the route from your position.
Yes, Dia's official website is www.dia.es. You'll find the direct link in the "Website" section of this listing.
On this listing you can see "Other supermarkets nearby" right below, sorted by proximity. You can also open the full supermarkets in Gualta page for the complete map ranked by distance from your location.