This parameter determines where to place the map on the page, and how large the map should be on the page.
The format for the parameter is four integers separated by spaces describing the lower left corner and the upper right corner of the viewport/rectangle, specified in typographical points. The lower left corner of the page has coordinate (0,0) and the top right corner has coordinate (<width>,<height>) where these two values are the page size specified by the parameter Page Size.
If the aspect ratios of the page viewport and the world viewport differ, then the lesser scaling factor will be chosen: data inside the world viewport will not be clipped and data outside the world viewport might become visible.
If a value for the parameter is not specified, then the page viewport rectangle will be a centered rectangle with a width and length that is 90% of the page width and length. The page viewport coordinates must be between (0,0) and (page width,page height).
Values: <lowerLeftX> <lowerLeftY> <upperRightX> <upperRightY>