The vector to raster error:

Vector polygons can be displayed continuously, where as raster layers are displayed as a series of pixels. This can create problems when converting from a vector to a raster, especially if the resolution (pixel size) is too large, an example would be the roads and river buffers shown below; they are showed as somewhat discontinued lines.

These two images depict the same area, the left being a raster, and the right being a vector. The “lines” in the raster are not continuous, partly because of the pixel size, another reason is the orientation of the lines (diagonal lines may not be continuous, but linked by corners instead).