Not sure I'm understand your question, but, basically, this is what Visio
does. If you go to the menu bar > View and select Size & Position Window.
Now, in your drawing, select a shape. The S&PW will show it's location (X &
Y), and size. At the bottom, it tells you where the "center" is located.
The default is the center of the shape. If you type new values in the S&PW
for X & Y, the shape will move and be centered on the new location.
If you open the shapes's shapesheet, menu bar > Window > Show ShapeSheet,
then, in the 1st section, Shape Transform, the entries for LocPinX & LocPinY
determine the shape's "origin". You may need to right click in the
ShapeSheet and select "Formulas". Visio actually draws the shapes based upon
width & height, but location is determined as above. See this entry for a
"graphical" display of LocPin definitions:
http://www.visguy.com/shapes/visio-art/. Scroll down to: Pin and LocPin
Illustration.
Sorry for the long answer!
HTH
Wapperdude