[NTG-context] Positioning graphics at positions on a page

[David Arnold]

Hi,

Measuring from the top left hand corner of US letter paper, I'd like  
to position four identical metapost graphics, centered at (2in,2in),  
(6in,4in), (2in,6in) and (6in,8in). The first entry in each pair is  
the amount I'd like to move to the right from the top left corner of  
the page. The second entry is the amount I'd like to move down from  
the top left corner of the page.

Any ideas?