Vector graphics is the use of polygons to represent images in computer graphics. Vector graphics are based on vectors, which lead through locations called control points or nodes. Each of these points has a definite position on the x- and y-axes of the work plane and determines the direction of the path; further, each path may be assigned various attributes, including such values as stroke color, shape, curve, thickness, and fill. At some point, a vector image is converted into a raster graphics image, which maps bits directly to a display space (and is sometimes called a bitmap). The vector image can be converted to a raster image file prior to its display so that it can be ported between systems.