Have you ever found yourself in a graphic pinch where you had to take an image normally meant for a business card and force it, in all its pixilated glory, onto a billboard? If not, all you need to know is that your average-sized image may not be up to the challenge because it's simply not scaleable.
Introducing: vector illustrations, your graphic hero when it comes to challenges of scale. To start, digital photographs are built differently than vectors. Look at a photo printed in yesterday's newspaper and hold it really close to your eyes. What do you see? Little colour dots, right? When you blow up an image all you're doing is making those little dots larger, which is why it's important to have a high number of pixels per inch when you're blowing up a photo.
Vector illustrations are totally different.
The information in a vector isn't stored in the number of colored dots or the pixels per inch it has. This means that you can make a vector as large as you like and it will remain crisp and sharp or what some call "resolution independent." That's why vectors are ideal for projects where you will have to scale your graphics between numerous sizes from what can fit in the palm of your hand, a card, to something you might have to slap on a wall-sized trade show booth.
The next best thing about vectors is how easy they are to manipulate because you can edit them over and over again without losing quality. They aren't one layer like photos, vectors are like a stack of colored paper which each have a different shape cut out of it. When you look at the pile, you'll see a bit of yellow from the sixth page in, covered by a blink of purple or a slice of green. Altogether, these multi-dimensional layers are each scalable but they all fit into one complex file of layers.