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

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> 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
>