Changing the Drawing Area Coordinate Origin

[Mark Jones <mark jones106 verizon net>]

Currently my drawing area's origin (x=0, y=0) is at the top left corner of 
the "canvas".  Since I am used to the Cartesian plane, this is not 
ideal.  I would like it to be the lower left corner.  Is there any way to 
do this?  Right now I am doing it by subtracing my y value from the 
vertical size, but I would rather not do it that way if it is possible.  Is 
the origin changeable?

Mark