Line thickness settings matter 
    
    In earlier versions of GrADS, line
  thickness setting between 1 and 5 always looked the same in the display and in image output -- only the vector graphics  formats would show any differences. With Cairo, each line thickness setting will  change the  rendered line thickness, not only for the vector graphics output, but also for  the X window display and  any image output. The anti-aliasing also allows for smooth, thin lines in the image output. However, thin lines that are less than one pixel wide may appear somewhat dim, with the color not fully saturated, because the color will always be partially blended with the background -- no single pixel will have the full color value. To compensate for this dimness, it is not advised to draw the lines twice, because of the problems mentioned above. It is better to tweak either the thickness setting or the RGB values of the color in order to achieve the desired effect of a bright yet thin line. 
    The default line widths for thickness settings between 1 and 12 are: 0.6, 0.8, 1.0, 1.25, 1.5, 1.75, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0. The units (pixels or points) will depend on the surface being drawn to -- pixels for the display window and image output, points for vector graphics. Use the new command set lwid to define a new line thickness setting if the 12 default widths are unsatisfactory.