Vector v.s Bitmap

     The difference between Vector and a Bitmap is that Bitmaps use pixels( tiny dots) and vector use mathematical equations known as scalable objects. Therefore when a image from Bitmap is blown up it will look blurry because the pixels will show and not blend. An image blown up in a Vector graph will come out more clear and defined because they are resolution independent.

Source : http://graphicssoft.about.com/od/aboutgraphics/a/bitmapvector_2.htm