Vector Graphics versus Raster Graphics
A vector graphics format uses descriptions of graphical objects like lines, rectangles, and circles to display an image. Vector images are displayed by rasterizing (converting) the description into a grid of colors that a modern display understand. All displays these days are a rectangular grid of pixels that can be individually tuned to show any color.
A raster image format stores images in a grid of colors. This is the same manner as required to display and this seems like a good way to do it. Indeed, raster image formats have been enormously successful because they are easy to display. Raster image formats are an obvious choice for storing photographs. After all, the universe is not full of arbitrary lines and circles that can be described as a vector graphic.
Vector graphics do have properties that recommend them. The most often cited is their ability to scale without becoming “blocky”. The scalability of vector graphics lends them to use where the same content will be displayed on multiple devices with different sized and shaped screens.
Vector graphics also lend themselves to being interactive as the properties of objects within the images can be rewritten on the fly to have them respond to the user. Sprites (individual raster images) are used to mimic this ability with raster images.
On one hand, a raster file is extremely easy to display (if it isn't scaled). On the other hand, all recent computers (even the kind in cell phones) are enormously powerful and programmers are generally quite clever. The additional work required to keep track of individual parts in a vector graphics file and creating the rasterized image for display is usually unnoticeable and can be well worth it.
SVG was created to provide a feature-rich vector graphics format for the web.