What is a Vector Graphic?
A vector graphic is one made up of points, lines and curves based on mathematical equations. It is used in contrast to a bitmap or raster graphic, which is made up of dots or pixels.
If you have ever tried to blow up an image such as a photo or logo and seen jagged edges and blurred text than you have seen a bitmap file. Vector artwork doesn’t have this problem. A vector file can be enlarged to any size without loosing quality. It is often created in adobe illustrator (.ai), macromedia freehand (.fhd) or corel draw (.cdr), where a bitmap file could come from just about anywhere, including digital cameras, scanners, or programs such at photoshop or paint. Some common bitmap file types are .jpg, .tif, or .gif.
When to use vector:
Logos especially should be vector, at least to start with. If you are having a logo designed it’s best to require that the master file be a vector file so that no matter what happens down the road, you have a file that will work. You can always create a bitmap file from a vector one, but it requires work and expertise to go the other way.
Anything that you want to enlarge in the future should be done either at it’s largest possible size in a bitmap file, or as a vector file so that you don’t end up with a quality problem if you choose to display them in a large format like on a billboard or sign in the future.
When to use bitmap:
Photos will always be bitmap because they require millions of colors to capture the actual photographic quality.
Online images are almost always bitmap. Many times they are exported from a vector graphic because it allows them to be the highest quality possible for the exact size that is to be displayed.