Vector images, also called object-oriented or draw images, are defined mathematically as a series of points joined by lines. Graphical elements in a vector file are called objects. Each object is a self-contained entity with properties such as colour, shape, outline, size, and position on the screen, included in its definition.
Since each object is self-contained, you can move and change its properties over and over again while maintaining its original clarity and crispness, and without affecting other objects in the illustration.
These characteristics make vector-based programs ideal for illustration purposes, where the design process often requires individual objects to be created and manipulated.
Vector-based drawings are resolution independent. This means that they appear at the maximum resolution of the output device, such as your printer or monitor. As a result, the image quality of your drawing is better if you print from a 600 dots per inch (dpi) printer than from a 300 dpi printer.
It is very easy to change the size of vector graphics without losing any of the detail, as happens with bitmap graphics. To demonstrate this, here is the artist animation from the top right corner of the page.
As you can see the image is still sharp, you just couldn't do that with a bitmap image. The other important factor is that the file size is exactly the same for the large image (it's actually the same file). With a bitmap image, because you can't simply re-scale it, you need to create a new image at the new dimensions, with a subsequent increase in file size.
The artist animation by the way, is a Shockwave file created using Macromedia's Flash and the file size is just 3 Kb.