There are two basic types of graphic files: Images and Vectors. Images are constructed from a series
of pixels, or tiny squares. Each pixel contains a unique colour and together they make up the image.
Vector images however have no pixels. They are displayed or printed by using mathematical
positioning. A vector image breaks down into a mathematical formula and contains messages like,
draw a rectangle, this size and at this place on the page. A vector image looks like an illustration.
Vector files are usually considerably smaller than a image files of the same image, since there is less
information required to achieve the same results.
Images however lose quality if they are scaled to a larger size. Basically when blown up the pixels
just get bigger. With vector images things are different the vector contains mathematical points that
map the shapes of the vectors. So vectors have no quality loss and no file size increase.
Note: you will rarely see an image used as a logo as when they are blown up they lose quality, most
logos are vector drawings.