A vector image basically  uses scalable shapes such as straight lines and curves, using coordinates and geometry to precisely define the parts of the image. and its more efficient than bitmaps at storing large areas of the same colour because it does not need to store every pixel as a bitmap does.

Vector graphics can be measured without it losing resolution. Also you can enlarged or reduced sizes the file will make not difference its basically the same 
 

Bitmap images are most imported images from cameras smartphones and online. Common bitmap image file types include JPEG, GIFand PNG. Bitmaps are also known as pixelmaps or raster graphics.

Bitmap images are organised as a grid of coloured squares called pixels (short for 'picture elements'). When zooming in or enlarging a bitmap image, the pixels are stretched and made into larger blocks. This is why bitmap images appear as poor quality when enlarged too much.