set coordinate system in canvas?

["Timothy H. Keitt" <Timothy Keitt StonyBrook Edu>]

I've been experimenting with the gnome canvas using the pygnome 
interface.  I'm wondering if there is a way to define the coordinate 
system for the canvas.  I want to create a canvas of a certain size, and 
then say that the left edge is x = -180, the right edge is x = 180, the 
upper edge is y = 90 and so on.  Newly placed items should conform t 
this coordinate system.  Setting the scroll region does not seem to help 
here. Thanks.

Tim

--
Timothy H. Keitt
Department of Ecology and Evolution
State University of New York at Stony Brook
Stony Brook, New York 11794 USA
Phone: 631-632-1101, FAX: 631-632-7626
http://life.bio.sunysb.edu/ee/keitt/