You tell Visio to expand the drawing to fit a large size printed page by selecting the Fit to 1 sheet(s) across by 1 sheet(s) down option on the Print Setup tab in the Page Setup dialog box.
By setting the drawing to fill one printed page, you are telling Visio to expand the drawing proportionally when it prints so that the drawing fills up as much of the large page as possible without distorting the drawing content.
Because the drawing expands proportionally, it may not be centered on the printed page, or there may be too much (or not enough) white space surrounding the drawing. You can preview the drawing before you print and then make the necessary adjustments.
The next screen describes how to preview and make adjustments to a drawing.