difference?

Since it came up in class today and since I'm not very articulate whenever I talk in front of my classes, I thought I'd try and explain the differences between the specifics of Production Designer & an Art Director again for anyone who's interested.
In the real world (aka not at USC because here there are many more responsibilities thrown onto the PDs), a Production Designer is someone who is in charge of creating the overall look of a film, designing its aesthetics and planning the way its visuals will look in the end. They work directly with the director to come up with locations and settings for the story to take place and the style that it will all happen in. They also work with the DP to establish the visual look. Production Design, as a department, is in charge of a ton of things, such as the Art Direction (which I will explain in a second), Production Illustrators (concept artists, storyboard artists), set decoration, the prop crew, set dressing, and working closely with the costume designers. Art Direction is the specific section of the crew that supervises set construction (anything from building to painting, greenspeople, sign painters, prop makers, various tradespeople, etc etc). The Art Director works directly under the Production Designer as liaisons to other departments, an authoritative figure dealing with administrative aspects as well as anything and everything to help the Production Design team to create their (and the director's!) vision.

Here are some images from Blade Runner, one of my all time favorite films, as well as a (groundbreaking) masterpiece in terms of production design. (including the still at the top of the entry!)