As you use the splitter in the XSLT mapper to widen the source and target document panes, the size of the mapper canvas is reduced. The Fit in Mapper Canvas button (
), located at the top of the XSLT mapper, redraws the diagram in whatever space is currently available to the mapper canvas. This feature is also available from the mapper short-cut menu (right-click anywhere on the mapper canvas to display the short-cut menu).