Layers are simultaneous, over– lapping components of an image or sequence. They are at work in countless media software programs, from Photoshop and Illustrator to audio, video, and animation tools, where multiple layers of image and sound (tracks) unfold in time. Maps use overlapping layers to associate and separate different levels of data, allowing each level to contribute to the whole while maintaining its own identity. Printing techniques use multiple layers of ink to build a single image. Although the layered archeology of the printed page or digital file tends to disappear in the final piece, experimental work often uncovers visual possibilities by exposing layers.