How do you know thats Riften? And I think you've got Solitude and Riverwood mixed up... maybe.
Solitude was confirmed to be the city on the rock bridge in a magazine about a month ago, though I haven't been able to find the source lately. Additionally, much anolysis went into deciding that it was Solitude months ago, and I'm pretty damn confident.
Riverwood is named as such in the URL of the link as well as in the demo. That "Riften shot" is named as such on the official Bethesda site (though not in the particular version of the image I linked).