how to generate image no border or unfilled area with GrADS?

[z z]

hi all
I am trying to create an output with no border area and axies, just
data map. Is there a way to do so and yet still maintain the
proportion of the map area. For example, I want to create a result
image of W 500 X H400 (W:H 1:1.25) for area of long:-67 to long -62,
and lat 42 to lat 46 (also W:H 1:25). I am expecting an image with no
border or unfilled area. I just can not figure out a way to do so.

Thanks advance