Most files you deal with on a daily basis are what is called a raster file. These are images made up of many colored blocks, or pixels, that come together to form a complete image. These are your jpg, png, gif and tif files. While these files can be printed at a high DPI, there is still a fixed number of pixels in that image, and that makes resizing the image to a larger size harder. By adding more pixels, a new color needs to be added, and program you are using to do so has to decide what color to add based on the surrounding pixels. This is what causes the image to look muddy or pixelated. This is where Vector files excel.
Vector files aren't based on pixels. They are based on dots, and how those dots are located in relation to the other dots in that image. Using mathematical formulas, a vector file increases or decreases the space between the dots proportionally as you resize it. This means that a 5" by 5" vector image can get resized to the size of a billboard without becoming pixelated or muddy in the slightest. These file types are ai, eps, svg, and sometimes pdf. You will find that most logos and other brand graphics are made in a vector format so that they can be used on anything from a business card to a large banner and more.
How is a vector image made?
A lot more goes into the creation of a vector image than opening up a jpg in Adobe Illustrator and saving it as an ai file. Doing so just creates another raster image. Instead, it takes using such a program to outline and create those dots and lines that make up a vector file. This can be a quick easy process, or a long and arduous one, depending on the complexity of the image. That is why designers prefer to create such files in vector first, and then export them to raster images later if possible and necessary. If you aren't sure what kind of file you have, we can help you with that, as well as give you an idea of what it would take to get you a vector format if necessary.
If you have any other questions about vector files, please email our designers at firstname.lastname@example.org. We would be happy to help you!