Vector Graphics offer superior quality as compared to other image formats such as Bitmap. For example, if you view a vector graphic and a bitmap picture and zoom them simultaneously, you will see that bitmap image has lost the quality however vector graphic's quality is still same. So, basically, Vector graphics keep the quality within an image and do not lost it even you zoom the images.
Its kind of hard practice to find websites giving you free vector graphics or vectors in public domain. You don’t have to spend your precious time to look for such websites as I have already done this job for you. Here are 10 best websites where you can find free vector graphics that are editable in Adobe Photoshop and Illustrator.