Probably executed using a projector from a fixed viewing point, then painting in the areas designated by the projection. More pictures at the link. The real question (for me, anyway) is does the project look its best when shown from fragments leading towards the whole, as my source blog chooses to present it, or is it better viewed from the whole into fragments? Which tells a better story? Obviously, fragments -> whole best represents a visitor's actual experience at the site. So why do I like seeing the whole first better?