[gradsusr] How to match land-ocean boundaries?

[Arlindo Meque]

I am plotting the precipitation field from CRU data.
Is there any function that will make my variable to match the
political boundary on the eastern side of the map? Please find attached the plot.
It seems that the precipitation field does not follow exactly the coastal line. 
I hope my question is clear.
Best regards,
Arlindo 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20111202/8151b715/attachment-0003.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: precipitation.png
Type: image/png
Size: 108842 bytes
Desc: not available
Url : http://gradsusr.org/pipermail/gradsusr/attachments/20111202/8151b715/attachment-0003.png