Visual aids can be used to encourage learning through sight and include print materials like textbooks, as well as non-projected materials like pictures, models and graphs. They can also be projected materials like slides and filmstrips. Examples of important visual aids discussed are textbooks, which should be appropriately graded and illustrative; maps and models for teaching places and processes; and the blackboard, which is widely used for writing and drawing. Other aids mentioned are pictures, flashcards, the epidiascope for enlarging images, educational television, filmstrips and slides, and the overhead projector.