No matter the type of mapping we’re undertaking, we run the danger of aliasing. Aliasing can ruin the appearance of a texture-mapped object. Aliasing is caused by undersampling. Two adjacent pixels in an object may not map two adjacent pixels in the texture map. As a result, some of the information from the texture map is lost when it is applied to the object.
Source : Teaching Texture Mapping Visually by Rosalee Wolfe / DePaul University / email@example.com