Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical equations, to represent images in computer graphics.
Vector graphics formats are complementary to raster graphics, which is the representation of images as an array of pixels, as is typically used for the representation of photographic images. Vector graphics are stored as mathematical expressions as opposed to bit mapped graphics which are stored as a series of mapped 'dots', also known as pixels (Picture cells).
That doesn't exactly translate, does it? Well, neither does me trying to explain that a vector graphic "is still shapes" and a raster graphic "is flat." I have no words. I rely on showing somebody on my computer screen.
My most recent foray into vector graphics involved my veterinarian's office. Rainbow City Pet Clinic is one of the four sponsors of GT Preps. All of the promotions (ads, business cards, mini-footballs) for GT Preps include the sponsors' logos.
I was emailed two copies of the RBC Pet Clinic logo to work with. One was a JPG that had been pulled off the website. And the second one was where somebody opened an Adobe Illustrator document, placed the JPG from the web, converted it to grayscale and then saved the image as an EPS.
(Placing a raster image on a page and then saving the document as an EPS or PDF will not magically make it into a vector graphic. Just so you know.)
But I had a font similar to the one used in the logo, so I was able to re-create a reasonable facsimile. La-dee-dah, problem solved.
Until the sales rep for RBC Pet Clinic informed me they have a new logo and sent me a JPG. By then, all of the promos were built. I had used the logos in white over a black field. I needed a vector version of the logo.
Rarely does anybody know what I'm talking about when I say I need vector. I used to ask for an EPS or a PDF, because I felt like if the company had maybe a disk with various versions of their logo, then send me the one that ends .EPS or .PDF, y'know?
But the file format is not the issue. Sometimes, you need the lines. The shapes. The "geometrical primitives" as per the Wiki.
Imagine if I had tried to call the vet's office myself.
"Rainbow City Pet Clinic, how may I help you?"
"Yeah, hi. I work at the Times. I need to speak with a manager or somebody who knows anything about you guys buying ads and/or contracting designers to update your logo. Because that's who I really need to speak with: the person who made your logo. They'll have what I need and know what I'm talking about."
I don't know how it went down, but when I got to work a few days later, I had an email from the sales rep. The attachment's file name included "logo_final.eps" and I crossed my fingers.
And just because I might need again, yet another attempt to explain the difference:
The difference between vector and raster graphics is that raster graphics are composed of pixels, while vector graphics are composed of paths. A raster graphic, such as a gif or jpeg, is an array of pixels of various colors, which together form an image. A vector graphic, such as an .eps file or Adobe Illustrator? file, is composed of paths, or lines, that are either straight or curved. The data file for a vector image contains the points where the paths start and end, how much the paths curve, and the colors that either border or fill the paths. Because vector graphics are not made of pixels, the images can be scaled to be very large without losing quality. Raster graphics, on the other hand, become "blocky," since each pixel increases in size as the image is made larger. This is why logos and other designs are typically created in vector format -- the quality will look the same on a business card as it will on a billboard.