File textures are bitmap images that filter better than most procedural textures and can result in better image quality.
You can bake an entire branch of a shading network to use the illumination, shadow, shading, and textures as a file texture (texture map) to obtain lighting effects that would be difficult to achieve in other ways. For more information, see Baking illumination and color.
Square vs. non-square bitmap images
You want your texture to fit your model perfectly, as though the texture has been painted on. You could measure the surface to which the texture is attached. However, because Maya LT is more efficient if it scales any non-square texture into a square texture, using a square image to begin with is recommended. If the object you are texturing is not square, for example, a lamp pole, place your texture in a black square.
