I made a post about this a long time ago but can't find it at the moment.
Basically the Visio drawing display surface has a maximum number of pixels
that can be shown (32K by 32K). An entire page is shown on the display
surface, although you may only see a portion of this in the window depending
on your zoom factor.
When a page is very large, Visio is unable to zoom into the diagram very far
because that would require it to generate a display image that exceeds 32K x
32K. The limitation is tied to Win 9x operating systems that did not
support larger display areas. Visio 2003 requires Windows 2000 or later to
run, but Visio's renderer was not updated to take advantage of the newer
display limits. Hopefully this will be addressed in the future.
Also, the maximum zoom level is a function of your page size and the pixel
density (dots per inch) of your display.
--
Mark Nelson
Office Graphics - Visio
Microsoft Corporation
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